CSET Practice Test Subtest II Science

Physical Characteristics of Minerals

The physical characteristics of minerals include traits 
which are used to identify and describe mineral species. 
These traits include color, streak, luster, density, 
hardness, cleavage, fracture, tenacity, and crystal 
habit. 

Certain wavelengths of light are reflected by the atoms 
of a mineral's crystal lattice while others are absorbed. 
Those wavelengths of light which are reflected are 
perceived by the viewer to possess the property of 
color. Some minerals derive their color from the 
presence of a particular element within the crystal 
lattice. The presence of such an element can 
determine which wavelengths of light are reflected 
and which are absorbed. This type of coloration in 
minerals is termed idiochromatism; different samples 
of an idiochromatic mineral species will all display 
the same color. Other minerals are colored by the 
presence of certain elements in mixture. Different 
samples of such a species may exhibit a range of 
similar colors. Still other mineral species may usually 
be colorless, but may display several different and 
startling colors when trace amounts of impurities, 
or elements which are not an integral part of the 
crystalline lattice, are present. Coloration which is 
caused by the presence of an element foreign to 
the crystal lattice, whether in mixture or in trace 
amounts, is termed allochromatism. Certain elements 
are strong pigmenting agents and may lend vivid 
colors to specimens when they are present, whether 
as a part of the crystal lattice, in mixture, or as an 
impurity. These elements are termed the chromophores. 

Streak is the color which a mineral displays when it has 
been ground to a fine powder. Trace amounts of 
impurities do not tend to affect the streak of a mineral, 
so this characteristic is usually more predictable than 
color. Two different specimens of the same species 
may be expected to possess the same streak, whereas 
they may display different colors. 

Minerals are either opaque or transparent. A thin section 
of an opaque mineral such as a metal will not transmit 
light, whereas a thin section of a transparent mineral will. 
Typically those minerals which possess metallic bonding 
are opaque whereas those where ionic bonding is 
prevalent are transparent. Relative differences in opacity 
and transparency are described as luster. The 
characteristic of luster provides a qualitative measure of 
the amount and quality of light which is reflected from 
a mineral's exterior surfaces. Luster thus describes how 
much the mineral surface 'sparkles'. 

The property of density is defined as mass per unit 
volume. Certain trends exist with respect to density 
which may sometimes aid in mineral identification. 
Native elements are relatively dense. Minerals whose 
chemical composition contains heavy metals, or atoms 
possessing an atomic number greater than iron (Fe, 
atomic number 26), are relatively dense. Species which 
form at high pressures deep within the earth's crust are 
in general more dense than minerals which form at 
lower pressures and shallower depths. Dark-colored 
minerals are typically fairly dense whereas light-colored 
ones tend to be less dense. 

Hardness is defined as the level of difficulty with which 
a smooth surface of a mineral specimen may be 
scratched. Hardness has historically been measured 
according to the Mohs scale. Mohs' method relies upon 
a scratch test to relate the hardness of a mineral 
specimen to the hardness of one of a set of reference 
minerals. Hardness may also be measured according to 
the more quantitative but less accessible diamond 
indentation method. 

Cleavage refers to the splitting of a crystal along a 
smooth plane. A cleavage plane is a plane of structural 
weakness along which a mineral is likely to split. The 
quality of a mineral's cleavage refers both to the ease 
with which the mineral cleaves and to the character 
of the exposed surface. Not every mineral exhibits 
cleavage. 

Fracture takes place when a mineral sample is split in a 
direction which does not serve as a plane of perfect or 
distinct cleavage. A mineral fractures when it is broken 
or crushed. Fracture does not result in the emergence 
of clearly demarcated planar surfaces; minerals may 
fracture in any possible direction. 

The characteristic of tenacity describes the physical 
behavior of a mineral under stress or deformation. Most 
minerals are brittle; metals, in contrast, are malleable, 
ductile, and sectile. 

The term crystal habit describes the favored growth 
pattern of the crystals of a mineral species. The 
crystals of particular mineral species sometimes form 
very distinctive, characteristic shapes. Crystal habit 
is also greatly determined by the environmental 
conditions under which a crystal develops. 

Color

When different wavelengths of visible light are incident 
upon the eye they are perceived as being of different 
colors. Three different varieties of color receptors in 
the eye correspond to light possessing wavelengths of 
approximately 660 nm (red), 500 nm (green), and 
420 nm (blue-violet). The eye then interprets the color 
of incident light according to which color receptors 
have been stimulated. For example, if monochromatic 
light which stimulated the red and green color receptors 
equally and did not affect the blue-violet receptors was 
detected, then the eye would interpret this light as 
possessing a wavelength halfway between those of red 
and green light. The eye would therefore register an 
incident light wave with a wavelength of approximately 
580 nm and the viewer would percieve the incoming 
light as yellow. Incident polychromatic light which 
stimulated the red and green color receptors equally 
and did not affect the blue-violet ones would also 
be interpreted as yellow light, regardless whether or 
not the incoming light actually contained a 
component with a wavelength close to 580 nm. 
The incident polychromatic light might possess only 
a red and a green component of equal intensity; it 
would nevertheless be interpreted by the eye as 
yellow light. The phenomenon called color is thus a 
description of the differentiation by the eye between 
various wavelengths and combinations of 
wavelengths of visible light. 

When light is incident upon a mineral specimen, some 
wavelengths are absorbed by the atoms of the crystal 
lattice while others are reflected. Those wavelengths 
which were not absorbed are reflected off of the 
mineral's surfaces and enter the eye of the viewer. The 
color which is perceived by the viewer depends on the 
wavelengths of light which are reflected rather than 
absorbed by the mineral. The property of color in 
minerals is thus due to the absorption of particular 
wavelengths of light and the reflection of others by 
the atoms of the crystal lattice. 

The color exhibited by certain mineral species may 
depend upon which crystallographic axis is transmitting 
the light. Such species may demonstrate several 
different colors as light is transmitted along various 
different axes. This phenomena of directionally 
selective absorption is termed pleochroism. 

Idiochromatism and the Chromophores

The color of many mineral species is derived directly 
from the presence of one or more of the elements 
which constitute the crystal lattice. The color of such 
minerals is a fundamental property directly related to 
the chemical composition of the species. Minerals 
which exhibit this type of coloration are called 
idiochromatic minerals. Idiochromatic coloration is a 
property possessed by a mineral species as a whole. 
In such species color can successfully be utilized as 
a means of identification. 

Ions of certain elements are highly absorptive of selected 
wavelengths of light. Such elements are called 
chromophores; they possess strong pigmenting 
capabilities. The elements vanadium (V), chromium (Cr),
manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and
copper (Cu) are chromophores. A mineral whose chemical
formula stipulates the presence of one or more of these
elements may possess a vivid and distinctive color. 

Examples of idiochromatic minerals abound. For instance,
 the copper carbonate malachite is consistently green; 
the copper carbonate azurite and the copper silicate 
chrysocolla are each a distinctive and predictable blue. 
Rhodochrosite is always red or pink; samples of sulphur 
are a bright, recognizable yellow. 

Most minerals which are composed entirely of elements 
other than the chromophores are nearly colorless. 
However, certain specimens are sometimes observed 
to possess vivid coloration. Color in such instances is 
due to the presence of an impurity. If one of the 
chromophores is present within a mineral whose 
chemical formula does not include it, then the foreign 
element constitutes an impurity or a defect in the 
lattice structure. Coloration in minerals which is due to 
the presence of a foreign element is termed 
allochromatism. In such cases the color of the mineral 
may differ radically from the nearly colorless shade 
expected of the species. 

Some minerals demonstrate a range of colors due to the 
presence in mixture of one of the chromophores. For 
example, the substitution of a quantity of iron for zinc 
atoms within the crystal lattice of sphalerite (ZnS) 
implements a change from white to yellow in the color 
of the mineral. Proportionally larger inclusions of iron 
will progressively result in a brown and eventually a 
black mineral specimen. In such cases the color of the 
sample is directly proportional to the amount of the 
pigmenting element which is present in the crystal 
lattice. 

Not all allochromatism in minerals is due to presence of 
substantial amounts of a chromophore in mixture, 
however. The property of color may sometimes be highly 
dependent on the inclusion of trace amounts of impurities. 
The presence of even a minute quantity of a chromophore 
within the crystal lattice can cause a mineral specimen to 
exhibit vivid color. For example, trace inclusions of 
chromium (Cr) in beryl are responsible for the deep green 
of emerald, while the purple of amethyst is due to trace 
amounts of iron (Fe) in quartz and the pink of rose quartz 
is due to trace inclusions of titanium (Ti). Samples of the 
mineral corundum which include tiny amounts of chromium 
are deep red, and the gem is then called a ruby, while 
samples containing iron or titanium impurities produce 
blue gems termed sapphire. 

Trace amounts of an impurity do not affect the basic 
chemical composition or the chemical formula of a mineral, 
and thus do not affect its classification as a species. Trace 
amounts of the various chromophores, however, can cause 
several samples of a single species to differ radically in 
color. (Beryl, corundum, and quartz provide examples of 
this possibility.) Because it varies so widely, color is a 
property which is sometimes of little use in identification. 
However, the idiochromatic minerals are consistently of 
distinctive color. The green of malachite, the blue of 
azurite, the pink of rhodocrosite, and the yellow of sulphur 
are easily recognized and are therefore quite useful in the 
identification of these species. 

Streak

Streak is the color of a mineral substance when it has 
been ground to a fine powder. Typically an edge of the 
sample will be rubbed across a porcelain plate, leaving 
behind a 'streak' of finely ground material. The material 
in a streak sample thus consists of a powder composed 
of randomly oriented microscopic crystals rather than a 
lattice structure containing the uniformly oriented unit 
cells which compose a macroscopic crystal. 

Although color is a property which may vary widely 
between two different specimens of the same mineral, 
streak generally varies little from sample to sample. The 
presence of trace amounts of an impurity may radically 
affect the property of color in a macroscopic crystal 
because each unit cell is aligned within the crystal 
structure, thereby forming a diffraction grating. In a 
streak sample, however, each of the microscopic crystal 
grains of the sample is randomly oriented and the presence 
of an impurity does not greatly affect the absorption of 
incoming light. Because it is not typically affected by the 
presence of an impurity, streak is a more reliable 
identification property than is color. 

Luster

Minerals may be categorized according to whether they 
are opaque or transparent. A thin section of an opaque 
mineral such as a metal will not transmit light, whereas 
a thin section of a transparent mineral will. The 
absorption index of an opaque mineral is high. Light which 
is incident upon an opaque mineral such as a metal is 
unable to propagate through the mineral due to this high 
rate of absorption, and will thus be reflected. Opaque 
minerals typically reflect between 20% to 50% or more of 
the light incident upon them. In contrast, most of the 
light which is incident upon a transparent mineral passes 
into and through the mineral; transparent minerals may 
reflect as little as 5% of the incident light and as much as 
20%. Typically those minerals which possess metallic 
bonding are opaque whereas those where ionic bonding 
is prevalent are transparent. 

Relative differences in opacity and transparency are 
described as luster. The term luster refers to the 
quantity and quality of the light which is reflected 
from a mineral's exterior surfaces. Luster provides an 
assessment of how much the mineral surface 'sparkles'. 
This quality is determined by the type of atomic bonds 
present within the substance. It is related to the indices 
of absorption and refraction of the material and the 
amount of dispersion from the crystal lattice, as well as 
the texture of the exposed mineral surface. 

Minerals are primarily divided into the two categories of 
metallic and nonmetallic luster. Minerals possessing 
metallic luster are opaque and very reflective, possessing 
a high absorptive index. This type of luster indicates the 
presence of metallic bonding within the crystal lattice of 
the material. Examples of minerals which exhibit metallic 
luster are native copper, gold, and silver, galena, pyrite, 
and chalcopyrite. The luster of a mineral which does not 
quite possess a metallic luster is termed submetallic; 
hematite provides an example of submetallic luster. 

The property of streak can aid in distinguishing whether a
specimen has a metallic or a nonmetallic luster. Metals 
tend to be soft, implying that more powdered material 
may be obtained from the streak sample of a metal than 
a nonmetal. Metals are also opaque, transmitting no light. 
Minerals which possess a metallic luster therefore tend to 
exhibit a thick, dense, dark streak whereas those which 
possess a nonmetallic luster tend to produce a thinner, 
less dense streak which is also lighter in color. 

Adjectives such as "vitreous', 'dull', 'pearly', 'greasy', 
'silky' or 'adamantine' are frequently used to describe 
various types of nonmetallic luster. 

Dull or Earthy 

Minerals of dull or earthy luster reflect light very poorly 
and do not shine. This type of luster is often seen in 
minerals which are composed of an aggregate of tiny 
grains. 

Resinous 

A surface of resinous luster possesses a sheen resembling 
that of resin. Such materials have a refractive index 
greater than 2.0. Sphalerite (ZnS) demonstrates a 
resinous luster. 

Pearly 

Pearly luster appears iridescent, opalescent, or pearly. 
This is typically exhibited by mineral surfaces which are 
parallel to planes of perfect cleavage. Layer silicates 
such as talc often demonstrate a pearly luster on 
cleavage surfaces. 

Greasy 

A surface which possesses greasy luster appears to be 
covered with a thin layer of oil. A light-scattering surface 
which is slightly rough, such as that of nepheline, may 
exhibit greasy luster. 

Silky 

Silky luster occurs when light is reflected off of an 
aggregate of fine parallel fibers; malachite and serpentine 
may both exhibit silky luster. 

Vitreous 

Vitreous luster occurs in minerals with predominant ionic 
bonding and resembles the reflective quality of broken 
glass. The refractive index of such minerals is 1.5 to 2.0. 
Many silicates possess this type of luster; quartz and 
tourmeline both demonstrate vitreous luster. 

Adamantine or brilliant 

A brilliant luster such as the sparkling reflection of 
diamond is known as adamantine. Minerals of adamantine 
luster have high refractive indices (1.9-2.6) and are 
highly dispersive and translucent. Covalent bonding or 
the presence of heavy metal atoms or transition elements 
may result in adamantine luster. 

Density

The property of density is defined as mass per unit volume: 

µ = m/V
The geometric structure of the unit cell of a mineral 
determines the volume which it occupies. The masses 
of the atoms which compose the unit cell decree the 
mass of each cell. The identity of the atoms which 
compose the unit cell is specified by the chemical formula 
of the mineral. Density is therefore directly related to 
both the physical structure of the unit cell and the chemical 
composition of each species of mineral. 

One method of measuring the density of a sample entails 
the use of one dense liquid and another miscible liquid of 
lower density. A solution of the two substances is created 
in which a crystal of the mineral in question remains 
suspended and neither sinks nor floats. The weight of a 
known volume of the solution is then measured, and the 
density of the solution and thus the density of the crystal 
are calculated from this information. Bromoform (CHBr3, 
density 2.9 g/cm3), soluble in acetone; di-iodomethane 
(CH2I2, density 3.3 g/cm3), soluble in chloroform, CHCl3; 
and Clerici's solution (a solution of thallium formate and 
thallium malonate; density 4.4 g/cm3), soluble in water, 
are some heavy liquids and their solvents which are 
commonly used in this process. 

Density has historically been equated by mineralogists 
with the concept of specific gravity. Specific gravity is 
a unitless quantity which is defined as the ratio of the 
weight of a substance to the weight of an equal volume 
of water at a temperature of 4° Celsius. This ratio is 
equal to the ratio of the density of the substance to the 
density of water at 4° Celsius. 

G = µ / µwater
Specific gravity has therefore classically been measured 
by weighing a mineral specimen on a balance scale while 
it is submerged first in air and then in water. The 
difference between the two measurements is the weight 
of the volume of water which was displaced by the 
sample. The specific gravity of the mineral specimen is 
thus: 

G = mair / [mair - mwater]
Because the density of water at 4° Celsius is 1.00 g/cm3, 
the density of a mineral in units of grams per centimeter 
cubed (g/cm3) is equal to its (unitless) specific gravity. 

The field geologist sometimes uses a very rough estimation 
of the density of a hand-held sample as a clue to 
identification. Certain rough trends relating mineral density 
to various other factors are sometimes useful. Native 
elements, which contain only one type of atom and whose 
molecular structure is that of cubic or hexagonal closest 
packing, are relatively dense. Minerals whose chemical 
composition contains heavy metals - atoms of greater 
atomic number then iron (Fe, atomic number 26) - are more 
dense than atoms whose chemical composition does not 
include such elements. Minerals which formed at the high 
pressures deep within the earth's crust are in general more 
dense than minerals which formed at lower pressures and 
shallower depths. A general trend relating color to density is 
also prevalent; this trend states that dark-colored minerals 
are often fairly heavy whereas light-colored ones are 
frequently relatively light. A geologist is thus given cause to 
remark upon a sample which seems to reverse this trend. 
For example, graphite is dark colored but of low density 
(C; 2.23 g/cm3) while barite is light in color but unexpectedly 
heavy (BaSo4; 4.5 g/cm3). The noted oddity of unexpectedly 
high or low density with respect to color provides the field 
geologist with a clue as to the identification of such atypical 
materials. 

Hardness
Hardness has traditionally been defined as the level of 
difficulty with which a smooth surface of a mineral specimen 
may be scratched. The hardness of a mineral species is 
dependent upon the strength of the bonds which compose 
its crystal structure. Hardness is a property characteristic 
to each mineral species and can be very useful in 
identification. 

Certain trends exist in hardness with respect to mineral 
class. (For a description of the various classes of minerals, 
please refer to the discussion on mineral classification 
contained in Section 4.) Native elements are typically soft, 
although iron (Fe) and platinum (Pt) are relatively hard and 
diamond (C) is exceptionally hard. Compounds of heavy 
metals are soft. Sulphides and sulpho-salts, with the 
exception of pyrite, are relatively soft; halides are soft; 
carbonates and sulphates are usually soft. Oxides are 
typically hard while hydroxides are softer. Anhydrous 
silicates tend to be hard, while hydrous silicates are 
softer. 

The Mohs Scale

The property of hardness has historically been measured 
according to the Mohs scale, which was created in 1824 
by the Austrian mineralogist Friedrich Mohs. Mohs based 
his system for measuring and describing the hardness of 
a sample upon the definition of hardness as resistance to 
scratching. Mohs' method thus relies upon a scratch test 
in order to relate the hardness of a mineral specimen to 
a number from the Mohs scale. 

In order to define his scale, Mohs assembled a set of 
common reference minerals of varying hardnesses and 
labled these in order of increasing hardness from 1 to 
10. The reference minerals of the Mohs scale are as 
follows: 

1. Talc 
2. Gypsum 
3. Calcite 
4. Fluorite 
5. Apatite 
6. Orthoclase 
7. Quartz 
8. Topaz 
9. Corundum 
10.Diamond 

Each reference mineral will scratch a test specimen 
with a Mohs hardness less than or equal to its own. 
Each reference mineral can be scratched by a specimen 
with a hardness equal to or greater than its own. If a 
reference mineral both scratches and can be scratched 
by a certain test specimen, then the specimen is 
assumed to possess a hardness equal to that of the 
reference mineral in question. 

The set of reference minerals of the Mohs' scale can be 
supplemented by a few common household items. A 
fingernail has a Mohs hardness of 21/2; a copper penny 
3, window glass 51/2, and a knife blade approximately 6. 

The hardness of an unknown sample can be determined 
to within 1/2 increment by using the scratch test. 
Mineral hardnesses determined by the scratch test 
should never be given in decimal form, because the Mohs 
scale does not provide measurements of such precision. 

The hardness of a mineral may vary with direction and 
crystallographic plane. This effect is usually small. 
However, species exist in which the variance in the 
hardness along different axes is notable. For example, 
the mineral kyanite (Al2OSiO4) typically forms elongated 
crystals. The Mohs hardness parallel to the length of a 
kyanite crystal is 5, whereas the Mohs hardness 
perpendicular to the length of such a crystal is 7. A second 
example is provided by the mineral halite, which is softer 
parallel to its cleavage planes than it is at a 45° angle to 
the cleavage planes. 

The Diamond Indentation Method

Investigations more recent than those completed by Mohs 
have used the diamond indentation method to quantitatively 
determine hardness. According to this method, a diamond 
point is pushed into a planar mineral surface under the 
weight of a known load. The diameter of the indentation 
thereby produced is then measured under a microscope. 
The diamond indentation hardness of a sample is equal to 
the mass of the load applied divided by the surface area 
of the indentation produced. The units in which diamond 
indentation hardness is recorded are therefore kilograms 
per millimeter squared (kg/mm2). 

Tests utilizing the diamond indentation method have shown 
that in order for a point fashioned from a certain material 
to scratch a surface the hardness of its constituent 
material must be 1.2 times that of the surface. Thus on 
an ideal hardness scale, each subsequent reference material 
would have a hardness of approximately 1.2 times that of 
the material preceeding it. It must be noted that the intervals 
between reference points on the Mohs scale are not, in fact, 
equal. The interval between subsequent reference points on 
the scale increases as the hardness of the reference 
materials increases. The skill with which Mohs chose his 
reference materials becomes apparent when one notes that 
each of his samples is approximately 1.6 times the hardness 
of the last. 

The Mohs scale provides a means of testing hardness 
which is far more readily available to amateur geologists 
than the diamond indentation method. It has therefore 
remained the standard scale by which hardness is 
measured. 

Cleavage
A cleavage plane is a plane of structural weakness along 
which a mineral is likely to split smoothly. Cleavage thus 
refers to the splitting of a crystal between two parallel 
atomic planes. Cleavage is the result of weaker bond 
strengths or greater lattice spacing across the plane in 
question than in other directions within the crystal. 
Greater lattice spacing tends to accompany weaker 
bond strength across a plane, because such bonds are 
unable to maintain a close interatomic spacing. 

Both the positioning of crystal faces in a mineral and the 
property of cleavage are derived from the crystalline 
structure of the species. However, despite the fact that 
every mineral belongs to a specified crystal system, not 
every mineral exhibits cleavage. A mineral such as quartz 
may demonstrate beautiful, well-developed crystals and 
yet possess no distinct planes of cleavage. 

Cleavage planes, if they exist, are always parallel to a 
potential crystal face. However, such planes are not 
necessarily parallel to the faces which the crystal actually 
displays. Fluorite, for example, has octahedral cleavage 
yet forms cubic crystals. Nonetheless, the property of 
cleavage, if it is present, can offer important information 
about the symmetry and inner structure of a crystal. 

The quality of a mineral's cleavage refers to both the 
ease with which the mineral cleaves and to the 
character of the exposed cleavage surface. The quality 
of a sample's cleavage is typically described by terms 
such as 'eminent,' 'perfect,' 'distinct,' 'difficult,' 
'imperfect,' or 'indistinct.' 

'Eminent' cleavage describes the case in which cleavage 
always occurs readily and is in fact difficult to prevent 
from occurring. The mineral mica, for example, cleaves 
readily into thin, flat sheets. A mineral which 
demonstrates 'perfect' cleavage breaks easily, exposing 
continuous, flat surfaces which reflect light. Fluorite, 
calcite, and barite are minerals whose cleavage is perfect. 
'Distinct' cleavage implies that cleavage surfaces are 
present although they may be marred by fractures or 
imperfections. 'Difficult' or 'indistinct' cleavage produces 
surfaces which are neither smooth nor regular; samples 
possessing such cleavage tend to fracture rather than 
split. 

Cleavage may be determined by the examination of 
surfaces which have actually broken. It may also be 
determined by inspection of the interlacing systems 
of cracks which permeate the structure of certain 
specimens. These systems of cracks are beautifully 
apparent within transparent crystals such as fluorite 
or calcite. 

Fracture

A mineral fractures when it is broken or crushed. 
Fracture takes place when a mineral sample is split 
in a direction which does not serve as a plane of 
perfect or distinct cleavage. In other words, fracture 
takes place along a plane possessing difficult, indistinct, 
or nonexistant cleavage. The difference between 
fracture and indistinct cleavage is not clearly 
delineated. 

Unlike perfect or distinct cleavage, fracture does not 
result in the emergence of clearly demarcated planar 
surfaces which run parallel to possible crystal faces. 
Fracture is nondirectional: minerals which do not 
possess distinct cleavage may fracture in any possible 
direction. 

Fractured surfaces may in some minerals possess a 
characteristic appearance which can aid in 
identification. Examples of distinctive types of fracture 
are 'conchoidal,' 'irregular,' and 'hackly' fracture. 

Conchoidal 

Conchoidal fracture results in a series of smoothly curved 
concentric rings about the stressed point, generating a 
shell-like appearance. The familiar ripples of a broken glass 
bottle demonstrate this type of fracture. Quartz and olivine 
are two mineral species which possess conchoidal
fracture. 

Irregular 

Irregular or uneven fracture results in a rough, rugged surface. 

Hackly 

The term 'hackly' describes a fractured surface with multiple 
small, sharp and jagged irregularities. 

Tenacity

The property of tenacity describes the behavior of a 
mineral under deformation. It describes the physical 
reaction of a mineral to externally applied stresses 
such as crushing, cutting, bending, and striking forces. 
Adjectives used to characterize various types of mineral 
tenacity include 'brittle,' 'flexible,' 'elastic,' 'malleable,' 
'ductile,' and 'sectile'. 

Brittle 

Most mineral species are brittle, and will crumble or 
fracture under pressure or upon the application of a 
blow. Such materials break or powder easily. 

Flexible 

A mineral which is flexible rather than brittle will flex as 
opposed to breaking under the application of stress. 
However, a mineral which is merely flexible and not also 
elastic will be unable to return to its original shape when 
the stress is removed. Flakes of molybdenite and scales 
of talc are two substances which are flexible but 
inelastic. 

Elastic 

An elastic mineral will deform under external stress but 
will resume its original shape after the stress is removed. 
If it is bent, it will flex, but will return to its previous 
position when the stress dissappears. The mineral called 
mica is both flexible and elastic. 

Malleable 

Native metals such as copper, silver, and gold are easily 
flattened with a hammer. This type of tenacity is 
termed malleable. Metallic-bonded minerals tend to be 
malleable, and may be pounded out into thin, flat sheets. 

Ductile 

Some malleable materials are also ductile, and may be 
drawn out into a thin wire without crumbling. 

Sectile

Some minerals may be sliced into smooth sheets with a 
knife, although these may possibly still crumble under a 
blow from a hammer. Materials possessing this rare type 
of tenacity are called sectile minerals. The species 
chlorargyrite (AgCl) offers an example of a sectile 
mineral. 

Crystal Habit

The term crystal habit describes the favored growth 
pattern of the crystals of a mineral species, whether 
individually or in aggregate. It may bear little relation 
to the form of a single, perfect crystal of the same 
mineral, which would be classified according to 
crystal system. (Please see the following discussion of 
crystal system in Section 3.) Subtle evidence of the 
crystal system to which a mineral species belongs is, 
however, frequently observed in the habit of the 
crystals which a specimen displays. 

The terminology used to describe crystal habit is not 
intended to replace the precise nomenclature of 
crystallography. Instead, it is intended as a supplement 
to this system. Discussions of crystal habit are more 
descriptive than precise; for this reason the terminology 
is suited to the discussion of mineral samples discovered 
in the field. Naturally formed specimens are rarely 
quantitatively perfect. 

The crystals of particular minerals species sometimes 
form very distinctive, characteristic shapes. Crystal 
habit is thus often useful in identification. 

Although each mineral species typically forms according 
to a few preferred shapes, crystal habit is largely 
determined by the environmental conditions under 
which a crystal develops. For example, aqueous 
solutions near or surrounding a crystal contain the 
elemental substances which it needs to continue 
growth. The direction from which a growing crystal 
may obtain such solutions is a factor which will affect 
its eventual shape. Higher environmental temperatures 
during formation increase ion mobility and aid in 
crystal formation; the rate at which the environment 
cools determines how much time a mineral is allowed 
to form large crystals. The amount of space available 
for a crystal to fill affects its final shape and size. 
Surface energy relations are also quite important to 
the direction of crystal growth; this process is not yet 
fully understood. 

Adjectives used to describe the habit of individual 
crystals are 'equant,' 'prismatic,' and 'tabular.' 
Aggregates of crystals may also be termed equant or 
prismatic, while aggregates of thin, flat, tabular 
crystals may be 'bladed.' Thin sheets, flakes or scales 
are termed 'foliated,' 'micaceous,' and, if feathery or 
delicate, 'lamellar' or 'plumose.' Crystal aggregates 
resembling long, slender needles, hair, or thread are 
termed 'acicular,' filiform,' 'capillary,' or 'fibrous.' An 
aggregate of crystals forming a network or lattice is 
'reticulated;' one composed of branches which radiate 
starlike from a central point is 'stellated' while a 
branching and treelike mineral growth is 'dendritic.' 
'Colloform' crystal habits termed 'botryoidal,' 'mamillary,' 
and 'reniform' display spherical, bulbous or globular 
lumps. Smaller spherical forms are of 'pisolitic' or 'oolitic' 
habit; ovoid clusters or formations are 'amygdaloidal.' 
Tapered, column-like formations are 'stalactitic' or 
'columnar' while concentrically banded formations are of 
'concretionary' habit. Minerals whose flat crystal faces 
are covered with shallow, parallel grooves are 'striated;' 
a fine furry layer of crystals growing over a massive 
lump constitutes a formation of 'drusy' habit. Following 
is a list of descriptive terms which are applied when 
discussing crystal habit. 

Equant 

A crystal which is equant or equidimensional possesses 
approximately the same side length in every direction. 
Crystals of garnet are often of equant habit. 

Prismatic 

A prismatic crystal is elongated in one direction like a 
prism. The mineral tourmaline often forms crystals of 
such habit. 

Tabular 

Tabular crystals appear tabular or platelike in shape. 

Bladed 

A specimen displaying bladed habit possesses a collection 
of elongated, flat crystals suggestive of knife blades. 
Gypsum often displays crystals of bladed habit. 

Foliated 

Crystals of foliated habit are separable into leafy structures 
or display leaflike projections. The word 'foliated' is 
derived from the Latin term folium, meaning 'leaf.' 

Micaceous 

Minerals of micaceous habit form as thin, flat sheets or 
flakes which are easily peeled or split off the larger mass. 
Muscovite provides an example of micaceous habit. 

Lamellar or lamelliform 

Crystals of lamellar habit form thin scales or plates which 
may resemble gills or lamellae. The term is derived from 
the Latin word lamina, meaning 'thin plate.' 

Plumose 

A mineral specimen of plumose habit displays fine, feathery 
scales resembling plumes. 'Plumose' is derived from the 
Latin term pluma, or 'feather.' 

Acicular 

The adjective 'acicular' means needlelike in shape. An 
acicular aggregate of crystals contains many long, 
slender crystals which may radiate out like needles or 
bristles from a common base. Acicular crystals are 
typically long and narrow like a pine leaf and seem to 
possess a sharp point. The mineral natrolite often 
exhibits acicular crystals. 

Capillary 

An aggregate of crystals of capillary habit resembles an 
intricate network of tubules. Capillary crystals appear 
long, slender, and fine, like delicate hairs. The term 
'capillary' is derived from the Latin word capillus, 'hair.' 

Filiform 

A mineral possessing crystals of filliform habit exhibits 
many hairlike or threadlike filaments. "Filiform' is derived 
from the Latin word filum, 'thread.' 

Fibrous 

Specimens possessing fibrous habit exhibit clumps of 
sinewy, stringy, or hairlike fibers. 

Reticulated 

A mineral specimen of reticulated habit seems to display 
a lattice, net, or network of small crystals. The word 
'reticulated' is derived from the Latin term rete, or 'net.' 

Stellated 

A mineral of stellated habit possesses several branches 
which radiate outwards from the center in a pattern 
resembling a star. The word 'stellated' stems from the 
Latin term stella, or 'star.' 

Dendritic 

Dendritic crystals form a divergent branching structure 
reminiscent of an arborescent, organic growth such as 
a tree or a dendrite. Native copper sometimes exhibits 
this habit. 

Colloform 

Specimens of colloform habit exhibit spherical, rounded, 
or bulbous shapes. Botryoidal, reniform, and mammillary 
habits are subsets of this category. 

Botryoidal 

The word 'botryoidal' means 'resembling a bunch of grapes,' 
or globular. Specimens of malachite frequently provide 
examples of botryoidal crystals. The Greek word botrus, 
'bunch of grapes,' provides the linguistic root of botryoidal. 

Mammillary 

Samples possessing mammillary crystal habit display soft, 
rounded curves. 

Reniform 

Reniform crystal habit displays the shape of a kidney. The 
mineral species hematite provides samples which exemplify 
both mammillary and reniform habit. 'Reniform' is derived 
from the Latin renes, 'kidney.' 

Oolitic 

Crystals of oolitic habit form small spheres or grains which 
resemble fish roe. Oolites are often found in limestones. 

Pisolitic 

A mineral of pisolitic habit develops round, pea-shaped 
forms. These are larger and slightly more uneven than 
an oolite and are usually composed of calcium carbonate. 
The word 'pisolitic' is derived from the Greek term pisos, 
'pea.' 

Amygdaloidal 

A mineral of amygdaloidal crystal habit demonstrates small 
almond-shaped nodules called amygdules. The term stems 
from the Latin word amygdala, or 'almond.' 

Stalactitic 

Stalactitic or columnar crystal habit refers to the tall, 
tapered, columlike appearance of an icicle or a limestone 
stalactite. Such formations are built up by the dripping 
of mineral-laden solution. The minerals calcite and 
aragonite (CaC03) typically form stalactites. The term is 
derived from the Greek word stalaktos, 'dripping.' 

Concretionary 

A concretion develops when mineral matter is 
concentrically deposited around a nucleus and colored 
and banded layers are build up. Malachite often exhibits 
such formations. 

Striated 

Minerals whose crystals are of striated habit display 
shallow parallel grooves or lines along flat crystal faces. 
Pyrite often demonstrates square, striated crystals. 

Drusy 

A sample exhibiting drusy habit displays a surface covered 
with a fine furry layer of tiny crystals. 

Massive 

Massive or earthy habit describes a large, lumpy mass 
which has no apparent crystal form. In such a sample 
the crystals are too tiny to be observable by the eye 
and are interlocked and mingled; the specimen lacks 
visible crystals. 

Physical Characteristics of Quartz

Quartz is a fun mineral to collect. Its abundance on the 
Earth's surface is incredible and produces some wonderful 
varieties that don't even look like the same mineral. A 
collector must always be up on the many varieties of 
quartz and it sometimes embarrasses a collector to have 
collected too many specimens of such a common mineral. 
But nearly all collectors concede that you can never really 
have enough quartz specimens.

Color is as variable as the spectrum, but clear quartz is 
by far the most common color followed by white or cloudy 
(milky quartz). Purple (Amethyst), pink (Rose Quartz), 
gray or brown to black (Smoky Quartz) are also common. 
Cryptocrystalline varieties can be multicolored. 
Luster ......: vitreous
Color .......: clear & white common (allochromatic)
all other colors are possible
Streak ......: white scratch
Breakage ....: conchoidal fracture.
Hardness ....: 7.0
Specific grav: ( 2.6) low
Other feat...: many kinds of luminescence & electricity. 
Hexagonal crystals have pyramid on one end, irregular 
fracture on the other. May have irregular but parallel
striations perpendicular to long axis
Habit .......: massive, crystalline or microcrystalline
Remarks .....: hard, lack of cleavage is most diagnostic,
but crystal form helps, also known as
AGATE, AMETHYST, CHERT, FLINT, JASPER.
Uses ........: electronics industry, computer chips
raw material for glass; jewelry; flux in metallurgy

Physical Characteristics of Calcite

Color ranges from colorless (very common) to beige, pale
brown, pale green and yellow (pale to lemon; the most 
common color).

Luster ......: vitreous - resinous
Color .......: white, any other color (allochromatic)
Streak ......: white
Breakage ....: 3-fold, non-perpendicular (rhombohedral) 
cleavage
Hardness ....: 3.0
Specific grav: ( 2.7) low
Other feat...: effervesces in cold HCl
birefringent when transparent
polysynthetic twinning: parallel to long diagonal
and edge of cleavage (see dolomite)
Habit .......: fine-grained masses (limestone);
cleavage masses (marble); xtalline aggregates;
cement of sedimentary rocks
Remarks .....: rhombohedral cleavage & effervescence in 
cold HCl diagnostic
Uses ........: important ingredients of cement;
limestone & marble: dimension stones of art and 
construction

Physical Characteristics of Hornblende

Luster ......: vitreous - shiny
Color .......: dark green, black
Streak ......: white scratch
Breakage ....: 2-fold (prismatic) clv. (56 o - 124 o )
Hardness ....: 6.0
Specific grav: ( 3.0) med.
Other feat...: fibrous appearance due to continuous 
clv. & luster
Habit .......: common constituent of intermediate igneous 
rocks
Remarks .....: an amphibole; prismatic, nearly 60-120 clv. 
and shiny luster diagn.
Uses ........: varietal mineral of granite, diorite and others

Physical Characteristics of Mica

Luster ......: resinous - vitreous
Color .......: usually black
Streak ......: white
Breakage ....: perfect single (basal) cleavage
Hardness ....: 2.5 - 3.0
Specific grav: ( 3.0) low
Other feat...: elastic, pseudohexagonal crystals
Habit .......: individual scales or foliated masses
sometimes as book-like crystals
Remarks .....: single cleavage, black color
and elasticity diagnostic
Uses ........: varietal mineral of igneous rocks
large sheets once used in capacitors

The Heart and the Circulatory System
by Roger E. Phillips, Jr.

Confusion over the nature of the heart, the blood, and 
the role of the blood in the body had existed for centuries. 
Pliny the Elder, a Roman writer who lived from AD 23-79, 
and author of a 37-volume treatise entitled Natural 
History, wrote "The arteries have no sensation, for they 
even are without blood, nor do they all contain the breath 
of life; and when they are cut only the part of the body 
concerned is paralyzed...the veins spread underneath the 
whole skin, finally ending in very thin threads, and they 
narrow down into such an extremely minute size that the 
blood cannot pass through them nor can anything else but 
the moisture passing out from the blood in innumerable 
small drops which is called sweat." 

A century later Galen, a Greek physician who lived in 
the second century AD., spent his lifetime in observation 
of the human body and its functioning. Galen believed 
and taught his students that there were two distinct 
types of blood. 'Nutritive blood' was thought to be made 
by the liver and carried through veins to the organs, 
where it was consumed. 'Vital blood' was thought to be 
made by the heart and pumped through arteries to carry 
the "vital spirits." Galen believed that the heart acted 
not to pump blood, but to suck it in from the veins. Galen 
also believed that blood flowed through the septum of 
the heart from one ventricle to the other through a 
system of tiny pores. He did not know that the blood left 
each ventricle through arteries. 

Physicians, as well as citizens, of many cultures had their 
own beliefs concerning the nature of the heart and 
circulatory system. While the Greeks believed that the 
heart was the seat of the spirit, the Egyptians believed 
the heart was the center of the emotions and the 
intellect. The Chinese believed the heart was the center 
for happiness. Even our modern society continues to 
put emotions under the control of the heart, speaking of 
having a broken heart when a loved one leaves, or 
stealing one's heart around Valentine's Day. These beliefs 
continued to be taught and taken as law until an English 
physician named William Harvey challenged them in the 
late 1620's.

William Harvey was born in 1578 in Folkstone, England. 
The eldest of seven sons, Harvey received a Bachelor of 
Arts degree from Cambridge in 1597. He then studied 
medicine at the University of Padua, receiving his 
doctorate in 1602. By all measures, Harvey was 
successful. After he finished his studies at Padua, he 
returned to England and set up practice. He then 
married Elizabeth Brown, daughter of the court physician 
to Queen Elizabeth I and King James I. This put in him in 
position to be noticed by the aristocracy, and Harvey 
quickly moved up the ladder. Eventually, he became 
court physician to both King James I and 
King Charles I. 

While acting as court physician, Harvey was able to 
conduct his research in human biology and physiology. 
Harvey focused much of his research on the mechanics 
of blood flow in the human body. Most physicians of 
the time felt that the lungs were responsible for moving 
the blood around throughout the body. Harvey 
questioned these beliefs and his questions directed his 
life-long scientific investigations. 

Harvey's experiments involved both direct dissection 
and physiological experiments on animals. His 
observations of dissected hearts showed that the 
valves in the heart allowed blood to flow in only one 
direction. Direct observation of the heartbeat of living 
animals showed that the ventricles contracted 
together, dispelling Galen's theory that blood was forced 
from one ventricle to the other.Dissection of the septum 
of the heart showed that it contained arteries and veins, 
not perforations. When Harvey removed the beating 
heart from a living animal, it continued to beat, thus 
acting as a pump, not a sucking organ. Harvey also used 
mathematical data to prove that the blood was not 
being consumed. Removal of the blood from human 
cadavers showed that the heart could hold roughly two 
ounces of blood. By calculating the number of 
heartbeats in a day and multiplying this by two ounces, 
he showed that the amount of blood pump far exceeded 
the amount that the body could possibly make. He 
based this figure on how much food and liquids a person 
could consume. To Harvey, this showed that the 
teaching by Galen that the blood was being consumed 
by the organs of the body was false. Blood had to be 
flowing through a 'closed circuit' instead. Even though 
he lacked a microscope, Harvey theorized that the 
arteries and veins were connected to each other by 
capillaries, which would later be discovered by Marcello 
Malpighi some years after Harvey's death.

Harvey did not let the beliefs of Galen concerning the 
role of natural, vital, and animal spirits and their effects 
on physiology affect his objectivity. Instead, Harvey 
asked simple, pointed questions, the types of questions 
that even today are the hallmark of good scientific 
research. Harvey asked such questions as why did both 
the lungs and the heart move if only the lungs were 
responsible for causing circulation of blood? Why should, 
as Galen suggested, structurally similar parts of the 
heart have very different functions? Why did 'nutritive' 
blood appear so similar to 'vital' blood? These, and 
other, questions gave Harvey his focus. 

Harvey's lecture notes show that he believed in the 
role of the heart in circulation of blood through a 
closed system as early as 1615. Yet he waited 13 
years, until 1628, to publish his findings in his work 
Exercitatio anatomica de motu cordis et sanguinis in 
animalibus or On the Movement of the Heart and 
Blood in Animals. Why did he wait so long? Galenism, 
or the study and practice of medicine as originally 
taught by Galen, was almost sacred at the time Harvey 
lived. No one dared to challenge the teachings of Galen. 
Like most physicians of his day, William Harvey, was 
trained in the ways of Galen. Conformation was not 
only the norm, but was also the key to success. To 
rebel against the teachings of Galen could quickly end 
the career of any physician. Perhaps this is why he 
waited. 

Harvey's hesitation proved well-founded. After his work 
was published, many physicians and scientists rejected 
him and his findings. Using different assumptions of the 
amount of blood contained in the heart, scientists 
argued that the blood could indeed be consumed. 
Controversy raged for a full twenty years after 
publication of "On the Movement of the Heart and Blood 
in Animals." Yet, with time, more and more physicians 
and researchers accepted Harvey's hypotheses.

Like all good research, Harvey's work raised more 
questions than it answered. For example, if blood was 
not consumed by organs, how did different parts of 
the body obtain nourishment? If the liver did not make 
blood from food, where did blood originate? These 
questions, and others like them, directed the research 
of many investigations for many years to come. Medical 
practice in Harvey's time, however, changed little. Even 
though the mechanics of blood flow were understood 
now, the understanding of the causes of many diseases 
were still bathed in the mystery of spirits. In fact, the 
practices of bleeding, lancing, and leeching increased in 
the years following Harvey's work. On the positive side, 
medicine did make some advances, for it was during the 
seventeenth century that administering medicine 
through intravenous injections came into practice. 

William Harvey's classic work became the foundation for 
all modern research on the heart and cardiovascular 
medicine. It has been said that Harvey's proof "of the 
continuous circulation of the blood within a contained 
system was the seventeenth century's most significant 
achievement in physiology and medicine." Further, his 
work is considered to be one of the most important 
contributions in the history of medicine. Without the 
understanding of the circulatory system made possible 
by Harvey's pioneering work, the medical miracles that 
we think are commonplace would be impossible. Let's 
take a few moments to discuss the hearts and 
circulatory systems found in a variety of animals.

The Types of Circulatory Systems

Remember that the circulation of the blood serves to 
move blood to a site or sites where it can be 
oxygenated, and where wastes can be disposed. 
Circulation then serves to bring newly oxygenated 
blood to the tissues of the body. As oxygen and 
other chemicals diffuse out of the blood cells and into 
the fluid surrounding the cells of the body's tissues, 
waste produces diffuse into the blood cells to be 
carried away. Blood circulates through organs such as 
the liver and kidneys where wastes are removed, and 
back to the lungs for a fresh dose of oxygen. And then 
the process repeats itself. This process of circulation 
is necessary for continued life of the cells, tissues and 
even of the whole organisms. Before we talk about the 
heart, we should give a brief background of the two 
broad types of circulation found in animals. We will also 
discuss the progressive complexity of the heart as one 
moves up the evolutionary ladder. 

Many invertebrates do not have a circulatory system 
at all. Their cells are close enough to their environment 
for oxygen, other gases, nutrients, and waste products 
to simply diffuse out of and into their cells. In animals 
with multiple layers of cells, especially land animals, 
this will not work, as their cells are too far from the 
external environment for simple osmosis and diffusion 
to function quickly enough in exchanging cellular 
wastes and needed material with the environment. 

In higher animals, there are two primary types of 
circulatory systems -- open and closed. Arthropods and 
most mollusks have an open circulatory system. In this 
type of system, there is neither a true heart or 
capillaries as are found in humans. Instead of a heart 
there are blood vessels that act as pumps to force the 
blood along. Instead of capillaries, blood vessels join 
directly with open sinuses. "Blood," actually a 
combination of blood and interstitial fluid called 
'hemolymph', is forced from the blood vessels into large 
sinuses, where it actually baths the internal organs. 
Other vessels receive blood forced from these sinuses 
and conduct it back to the pumping vessels. It helps 
to imagine a bucket with two hoses coming out of it, 
these hoses connected to a squeeze bulb. As the bulb 
is squeezed, it forces the water along to the bucket. 
One hose will be shooting water into the bucket, the 
other is sucking water out of the bucket. Needless to 
say, this is a very inefficient system. Insects can get 
by with this type system because they have numerous 
openings in their bodies (spiracles) that allow the 
"blood" to come into contact with air. 

The closed circulatory system of some mollusks and all 
higher invertebrates and the vertebrates is a much 
more efficient system. Here blood is pumped through a 
closed system of arteries, veins, and capillaries. 
Capillaries surround the organs, making sure that all 
cells have an equal opportunity for nourishment and 
removal of their waste products. However, even closed 
circulatory systems differ as we move further up the 
evolutionary tree.

One of the simplest types of closed circulatory systems 
is found in annelids such as the earthworm. Earthworms 
have two main blood vessels -- a dorsal and a ventral 
vessel --which carry blood towards the head or the 
tail, respectively. Blood is moved along the dorsal 
vessel by waves of contraction in the wall of the 
vessel. These contractible waves are called 
'peristalsis.' In the anterior region of the worm, there 
are five pairs of vessels, which we loosely term 
"hearts," that connect the dorsal and the ventral 
vessels. These connecting vessels function as 
rudimentary hearts and force the blood into the 
ventral vessel. Since the outer covering (the epidermis) 
of the earthworm is so thin and is constantly moist, 
there is ample opportunity for exchange of gases, 
making this relatively inefficient system possible. There 
are also special organs in the earthworm for the 
removal of nitrogenous wastes. Still, blood can flow 
backward and the system is only slightly more efficient 
than the open system of insects.

As we come to the vertebrates, we begin to find real 
efficiencies with the closed system. Fish possess one 
of the simplest types of true heart. A fish's heart is a 
two-chambered organ composed of one atrium and 
one ventricle. The heart has muscular walls and a 
valve between its chambers. Blood is pumped from the 
heart to the gills, where it receives oxygen and gets 
rid of carbon dioxide. Blood then moves on to the 
organs of the body, where nutrients, gases, and wastes 
are exchanged. However, there is no division of the 
circulation between the respiratory organs and the 
rest of the body. That is, the blood travels in a circuit 
which takes blood from heart to gills to organs and 
back to the heart to start its circuitous journey again.

Frogs have a three-chambered heart, consisting of two 
atria and a single ventricle. Blood leaving the ventricle 
passes into a forked aorta, where the blood has an 
equal opportunity to travel through a circuit of vessels 
leading to the lungs or a circuit leading to the other 
organs. Blood returning to the heart from the lungs 
passes into one atrium, while blood returning from the 
rest of the body passes into the other. Both atria empty 
into the single ventricle. While this makes sure that 
some blood always passes to the lungs and then back to 
the heart, the mixing of oxygenated and deoxygenated 
blood in the single ventricle means the organs are not 
getting blood saturated with oxygen. Still, for a 
cold-blooded creature like the frog, the system works 
well.

Humans and all other mammals, as well as birds, have a 
four-chambered heart with two atria and two ventricles. 
Deoxygenated and oxygenated blood are not mixed. The 
four chambers ensure efficient and rapid movement of 
highly oxygenated blood to the organs of the body. This 
has helped in thermal regulation and in rapid, sustained 
muscle movements. 

On average, your body has about 5 liters of blood 
continually traveling through it by way of the 
circulatory system. The heart, the lungs, and the blood 
vessels work together to form the circle part of the 
circulatory system. The pumping of the heart forces 
the blood on its journey. 

The body's circulatory system really has three distinct 
parts: pulmonary circulation, coronary circulation, and 
systemic circulation. Or, the lungs (pulmonary), the 
heart (coronary), and the rest of the system (systemic). 
Each part must be working independently in order for 
them to all work together. 

In a general sense, a vessel is defined as a hollow 
utensil for carrying something: a cup, a bucket, a tube. 
Blood vessels, then, are hollow utensils for carrying 
blood. Located throughout your body, your blood vessels 
are hollow tubes that circulate your blood. 
There are three varieties of blood vessels: arteries, 
veins, and capillaries. During blood circulation, the arteries 
carry blood away from the heart. The capillaries connect 
the arteries to veins. Finally, the veins carry the blood 
back to the heart. 

If you took all of the blood vessels out of an average 
child, and laid them out in one line, the line would be 
over 60,000 miles long! An adult's vessels would be 
closer to 100,000 miles long! 

Besides circulating blood, the blood vessels provide two 
important means of measuring vital health statistics: 
pulse and blood pressure. We measure heart rate, or 
pulse, by touching an artery. The rhythmic contraction 
of the artery keeps pace with the beat of the heart. 
Since an artery is near the surface of the skin, while 
the heart is deeply protected, we can easily touch the 
artery and get an accurate measure of the heart's 
pulse. 

When we measure blood pressure, we use the blood 
flowing through the arteries because it has a higher 
pressure than the blood in the veins. Your blood 
pressure is measured using two numbers. The first 
number, which is higher, is taken when the heart 
beats during the systole phase. The second number 
is taken when the heart relaxes during the diastole 
phase. Those two numbers stand for millimeters. A 
column of mercury rises and falls with the beat of 
the heart. The height of the column is measured in 
millimeters. Normal blood pressure ranges from 110 
to 150 millimeters (as the heart beats) over 60 to 
80 millimeters (as the heart relaxes). It is normal for 
your blood pressure to increase when you are 
exercising and to decrease when you are sleeping. 
If your blood pressure stays too high or too low, 
however, you may be at risk of heart disease.

Pulmonary circulation is the movement of blood from 
the heart, to the lungs, and back to the heart again. 
This is just one phase of the overall circulatory system. 
The veins bring waste-rich blood back to the heart, 
entering the right atrium throughout two large veins 
called vena cavae. The right atrium fills with the 
waste-rich blood and then contracts, pushing the 
blood through a one-way valve into the right ventricle. 
The right ventricle fills and then contracts, pushing 
the blood into the pulmonary artery which leads to 
the lungs. In the lung capillaries, the exchange of 
carbon dioxide and oxygen takes place. The fresh, 
oxygen-rich blood enters the pulmonary veins and then 
returns to the heart, re-entering through the left 
atrium. The oxygen-rich blood then passes through a 
one-way valve into the left ventricle where it will exit 
the heart through the main artery, called the aorta. 
The left ventricle's contraction forces the blood into 
the aorta and the blood begins its journey throughout 
the body. 

The one-way valves are important for preventing any 
backward flow of blood. The circulatory system is a 
network of one-way streets. If blood started flowing 
the wrong way, the blood gases (oxygen and carbon 
dioxide) might mix, causing a serious threat to your 
body. 

You can use a stethoscope to hear pulmonary 
circulation. The two sounds you hear, "lub" and 
"dub," are the ventricles contracting and the valves 
closing. 

While the circulatory system is busy providing oxygen 
and nourishment to every cell of the body, let's not 
forget that the heart, which works hardest of all, 
needs nourishment, too. Coronary circulation refers to 
the movement of blood through the tissues of the 
heart. The circulation of blood through the heart is just 
one part of the overall circulatory system. 
Serious heart damage may occur if the heart tissue 
does not receive a normal supply of food and oxygen. 
The heart tissue receives nourishment through the 
capillaries located in the heart. 

Systemic circulation supplies nourishment to all of the 
tissue located throughout your body, with the 
exception of the heart and lungs because they have 
their own systems. Systemic circulation is a major 
part of the overall circulatory system. 
The blood vessels (arteries, veins, and capillaries) are 
responsible for the delivery of oxygen and nutrients to 
the tissue. Oxygen-rich blood enters the blood vessels 
through the heart's main artery called the aorta. The 
forceful contraction of the heart's left ventricle forces 
the blood into the aorta which then branches into 
many smaller arteries which run throughout the body. 
The inside layer of an artery is very smooth, allowing 
the blood to flow quickly. The outside layer of an 
artery is very strong, allowing the blood to flow 
forcefully. The oxygen-rich blood enters the capillaries 
where the oxygen and nutrients are released. The 
waste products are collected and the waste-rich blood 
flows into the veins in order to circulate back to the 
heart where pulmonary circulation will allow the 
exchange of gases in the lungs. 

During systemic circulation, blood passes through the 
kidneys. This phase of systemic circulation is known 
as renal circulation. During this phase, the kidneys filter 
much of the waste from the blood. Blood also passes 
through the small intestine during systemic circulation. 
This phase is known as portal circulation. During this 
phase, the blood from the small intestine collects in 
the portal vein which passes through the liver. The liver 
filters sugars from the blood, storing them for later. 

Summary

Red blood cells carry oxygen from the lungs to all the 
cells of the body. 
White blood cells are like soldiers protecting the body. 
ARTERIES are vessels that carry blood away from the 
heart. 
VEINS are vessels that carry blood back to the heart. 
Blood CIRCULATES--circles--all around your body in 
about one or two minutes. 
Inside the heart are four hollow chambers. Each 
chamber is a little pump. The pumping pushes blood 
all around your body.