Glossary of Terms
Used in These Pages
(al-lo-chro-ma-tic) The color of a mineral that results from mineral
impurity, such as minor chemical substitutions or radiation damage.
Allochromatic is the opposite of
(am'-ber) A fossil resin from coniferous trees. It is transparent,
usually yellow or brown, and may enclose insects or other organisms.
amorphous (a-mor'-phous) The state of a solid lacking a
crystal structure, specifically lacking long-range order.
andesite (an-de-site) A dark-colored to light gray,
fine-grained extrusive igneous rock that typically formed through the relatively
rapid crystallization of a lava. Andesites can also form through the
accumulation of pyroclastic material explosively erupted from a volcano.
Andesites are typically porphyritic or composed of two sizes of crystalline
material. The larger crystals or phenocrysts are composed primarily of zoned
sodic plagioclase (especially andesine) and one or more of the following mafic
minerals, biotite, hornblende, pyroxene, and are surrounded by a groundmass
consisting of finer-grained minerals of the same composition as the
phenocrysts but too small to be seen without a microscope. Andesites
contain more silica, aluminum, sodium, and potassium and less magnesium, iron,
and calcium than basalts. If an andesitic magmas undergoes magmatic
differentiation typically there will be an increase in Si, Al, Na, and K, and a
decrease in Mg, Fe, and Ca, dacite and ultimately rhyolite lavas could be
produced. Andesite was named after the Andes Mountains of South America.
(an'-i-on) A negatively charged ion.
anisotropic (an'-i-so-trop'-ic) Having
physical properties that vary in different directions. Characteristic of
all crystalline substances, including minerals, except those belonging in the
isometric system, which are isotropic.
apatite (ap'-a-tite) 1. A group of hexagonal minerals
consisting of calcium phosphate together with florine, chlorine, hydroxyl, or
carbonate substituting for the phosphate radical having the general formula Ca5
(PO4)3 (F,Cl,OH). Apatite occurs as accessory
minerals in igneous and metamorphic rocks, ore deposits; and most commonly as
fine-grained and often impure masses as the chief constituent of phosphate
rock. A material similar to apatite makes up bones and teeth.
mineral with the same composition as
calcite (CaCO3), but stable at
higher pressures. It occurs in hot-spring deposits, in coral reefs,
in the nacre of pearls, and in the shells of some
brachiopods formed at or near
The layer or shell of the Earth below the lithosphere (typically 70 to 100 km
down to a depth of 400 km) that deforms ductilely due to its low yield strength,
permitting viscous or plastic flow under relatively small stresses. The
asthenosphere is that part of the upper mantle in which isostatic adjustments
take place, magmas are generated, and seismic waves are strongly attenuated
(shortened or damped).
(at'-om) The smallest possible unit of a chemical element, consisting of
one or more protons and (except for
hydrogen) two or more neutrons located in
the nucleus, and one or more electrons
which revolve in orbits around the nucleus. Because the nucleus of each
atom contains the same number of positively charged protons as negatively
charged electrons, it is electrically neutral, or uncharged. Atoms of the
various elements differ in mass (weight), also expressed as the number of
neutrons and protons, as well as in the number of electrons. Atoms of a
given element are identical, but an element may have atoms of slightly different
masses, called isotopes. Isotopes vary only in their number of neutrons.
Atoms of the same or different elements combine to form molecules; when the
atoms are of two or more different elements these molecules are called
compounds. Atoms remain essentially unchanged in chemical reactions,
except that some of the outermost electrons may be removed, shared or
transferred, as occurs in ionization and chemical bonding.
bacteria (bac-te'-ri-a) Single-celled microorganisms
that lack chlorophyll (the green plant pigment essential to photosynthesis) and
an evident nucleus. Most bacteria are capable of decomposing or breaking
down organic matter.
(ba-salt') A dark-colored mafic (having a composition rich in iron and
magnesium) igneous rock, commonly extrusive but locally intrusive in dikes,
composed chiefly of calcic plagioclase and clinopyroxene, although nepheline,
olivine, orthopyroxene, or quartz may be present. Basalt is the
fine-grained equivalent of gabbro. Basalts typically have low viscosity
and therefore occur in lava flows.
biogenic (bi-o-gen'-ic) Formed by the action of
biotite NEED A DEFINITION.
birefringence () The magnitude
of the difference in the index of refraction of birefringent minerals i.e. that
is all minerals that are nonisotropic (All minerals that crystallize in the
tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic crystal systems).
birefringent () Having two or three refractive
indices. Minerals that crystallize in the tetragonal and hexagonal crystal
systems have two indices of refraction. Minerals that crystallize in the
orthorhombic, monoclinic, and triclinic crystal systems have three indices of
brachiopod (bra'-chi-o-pod) Any marine
invertebrate belonging to the
phylum Brachiopoda, and characterized by two bilaterally symmetrical (i.e.: both
sides the same size and shape) valves. Brachiopods most often attach
themselves to a substrate, but may also be free.
breccia (bre'-cchi-a) A coarse-grained clastic rock
(made of particals), composed of angular broken rock fragments held together by
a mineral cement or in a fine-grained matrix. Breccia differs from
conglomerate in that the fragments have sharp edges and unworn corners. Breccia
may originate as a result of talus accumulation, explosive igneous processes,
collapse of rock material, or faulting.
brilliance (brilliance) Degree to which a faceted
mineral or gemstone sparkles and returns light from within. Brilliance is
dependent on the cup and refractive index of the mineral.
calcareous NEED A DEFINITION.
calcite (cal'-cite) A common rock-forming hexagonal
mineral (CaCO3) that has
effervesces (bubbles) in cold,
dilute HCl acid.
carbonate NEED A DEFINITION.
carbonatite (car-bon'-a-tite) A carbonate rock of of
magmatic origin derived through partial melting of the upper mantle, generally
associated with alkalic igneous rocks. The carbonate material that makes
up many carbonatites is in part recycled sedimentary rocks that have been
returned into the mantle through subduction based on isotopic evidence.
(cat'-i-on) A positively charged ion.
Si4+, Fe2+, Fe3+ and V4+ are all
examples of cations.
The emission of light by a mineral caused by electron bombardment (CL is a type
of luminescence). Cathodoluminescence can be observed directly using
microscope-mounted systems or it can be recorded indirectly using electron
microbeam instumentation. Cathodoluminescence images of several minerals
captured with a scanning electron microscope (SEM) are available at
chatoyancy (chatoyancy) A cat's eye appearance to a
polished mineral when illuminated. Chatoyancy is caused by the parallel
arrangement of tiny needles or prisms within a crystal.
cleavage (cleav'-age) The tendency of a mineral to
break along specific crystallographic planes in all specimens because the
presence of directions of weakness in the crystal due to fewer or weaker
chemical bonds in those directions.
A combustible organic material containing more than 50% by weight and more than
70% by volume of carbonaceous (i.e.: rich in carbon) material, including
inherent moisture. Coal is formed through
induration of plant remains
similar to those in peat.
compaction NEED A DEFINITION.
contact metamorphism (con'-tact
met'-a-mor-phism) The metamorphic processes by which rocks at or
near their contact with a body of igneous rock are recrystallized or changed to
other minerals due to increases in temperature and materials emanating from the
magmas and by some deformation connected with the emplacement of the igneous
consolidated NEED A DEFINITION.
corundum NEED A DEFINITION.
Composed of submicroscopic crystals.
crystal (crys' tal) A solid body having a regularly
repeated long-range three dimensional internal arrangement of atoms.
The external expression of a crystal may be bounded, although it does not have
to be bounded, by natural planar surfaces called "faces".
crystalline (cryst'-tal-line) Having the properties
of a crystal, specifically a regularly repeated long-range three dimensional
internal arrangement of atoms.
crystallographic direction NEED A
cyclotron (cy'-clo-tron) An accelerator in which
ions are propelled by an alternating
electric field within a constant magnetic field to study the nature of matter.
sediments (de-tri'-tal sed'-i-ments) rock particles or mineral
fragments derived through the mechanical disintegration of preexisting parent
rocks either by erosion or by weathering. Also called clastic sediments or
detritus. Detrital sediments are classified according to the size
(boulder, cobble, sand, silt, and clay-sized) and nature of the material (lithic
or rock fragments, quartz, feldspar, clay minerals, heavy oxide minerals,
deuteron (deu-te-ron') The nucleus of the deuterium
atom, consisting of one proton and one neutron, also referred to as heavy
water. The nucleus of the deuterium atom is the same as the
isotope of hydrogen that has twice
the mass of ordinary hydrogen.
(di'-a-tom) A microscopic, unicellular (i.e.: single-celled) algae.
Diatoms are found almost everywhere, including marine, brackish, fresh water,
soil, and ice environments - and even hot springs. They secret
siliceous frustules or
exoskeletons in a great variety of forms.
diamond NEED A DEFINITION.
dispersion (dis-per'-sion) The systematic variation
of the index of refraction
with color within a substance, due to the fact that white light is composed of a
range of wavelengths. Minerals such as diamond with high dispersion are said to
have "fire" or the ability to split white light into its respective colors.
dolomite (do'-lo-mite) 1:
A common rock forming hexagonal mineral (CaMg(CO3)2)
with perfect rhombohedral
cleavage. Powdered dolomite
effervesces (bubbles) in cold dilute HCl acid.
sedimentary rock, composed of more than
50% by weight of the mineral dolomite. A dolomitic limestone (do-lo-mit'-ic
lime-stone) is a limestone in which the mineral dolomite makes up 10-50% of the
The process by which limestone is wholly or partly converted to dolomite rock,
or dolomitic limestone, by the replacement of the original
calcite by the mineral dolomite,
usually through the action of magnesium-bearing water (either sea water or
percolating meteoric water).
effervesce (ef-fer-vesce) The bubbling produced when carbon
dioxide (CO2)is liberated by the reaction of dilute HCl (hydrochloric
acid) and calcite (CaCO3) and powdered dolomite (CaMg(CO3)2)
or other carbonate minerals.
element (el'-e-ment) One of the 116 to 118 presently
known fundamental substances that consist of
atoms of only one kind, and that singly or in combination constitute all
matter. The most recently discovered elements are artificially produced by
atomic collisions of atomic particles in
cyclotrons, and exist for only fractions of a second before decaying to
electron (e-lec'-tron) A fundamental particle of
matter that can exist either as part of an atom
or in the free state. It has a negative electric charge (4.8 x 10-10
e.s.u.) and a mass 1/1837th that of a proton (about 9.1 x 10-28
gram). The number of electrons in an atom is equal to the number of
protons in the nucleus (also known as
the atomic number). Depending on
the position of an element in the Periodic Table, the electrons are arranged in
from 1 to 7 orbits (called shells), in which they revolve around the
nucleus. The maximum number of electrons in any shell is precisely limited
by the laws of physics.
(e-vap'-o-rite) A mineral or rock chemically precipitated directly from
evaporating sea or lake water in arid and semiarid regions. Gypsum,
halite, and sylvite are evaporite minerals.
feldspar (feld'-spar) The monoclinic or
triclinic minerals with the general formulae KAlSi3O8 -
K,NaAlSi3 O8 and NaAlSi3 O8 -
CaAl2Si2O8. The feldspar mineral group
contains two high-temperature series, the plagioclase series (albite, oligoclase,
andesine, labradorite, bytownite, and anorthite) and the alkali feldspar
series (sanidine, anorthoclase, orthoclase, and microcline). Barium
feldspars such as celsian and hyalophane are realatively rare. The
feldspar minerals are colorless, white, pink, salmon-pink, light or dark gray
and clear to translucent and commonly twinned by one or more twin laws.
Feldspar group minerals have two directions of cleavage that intersect at or
near 90o and a Mohs hardness of 6. Feldspars group minerals
compose 60% of the Earth's crust. Feldspar occurs in all rock types
and alters at atmospheric conditions to form clay minerals.
Division of colors in a colorless, transparent gemstone as a result of
fluorite (fluor'-ite) An isometric mineral, CaF2
with perfect octahedral cleavage that is typically
transparent to translucent and defines 4 on the Mohs hardness scale.
Fluorite occurs in hydrothermal veins
as a gangue mineral, in carbonate rock, and is an accessory in igneous rocks.
(gangue) A mineral without economic value that is part of an ore deposit.
Quartz, calcite, and fluorite are common gangue minerals.
A state of matter intermediate between the close-packed, highly ordered array of
atoms in a crystal and the poorly packed, highly disordered array of atoms in a
gas. Most glasses are supercooled liquids but there is no clear dividing
point in the range of properties between the metastable and stable states.
The distinction between glass and liquid is on the basis of viscosity, or how
much internal resistance the material offers to flow.
granite (gran'-ite) 1. A course-grained plutonic rock
in which quartz constitutes 10% to 50% of the felsic components and in which the
alkali feldspar/total feldspar ratio is generally restricted to the range of 65%
to 90%. Rocks in this range of composition are scarce, and sentiment has
been growing to expand the definition to include rocks designated as adamellite
or quartz monzonite, which are abundant in the United States. 2. Broadly
applied, any holocrystalline (totally crystalline), quartz-bearing plutonic
rock. For more information on granite, see
Rob's Granite Page.
(gyp'-sum) A monoclinic mineral (CaSO4 .2H2O) that
is colorless to white in crystals but gypsum in massive beds may range from red
to yellow to brown, gray, or black. It is the most common natural sulfate
mineral. Gypsum defines 2 on the Mohs hardness scale. It is commonly
associated with rock salt (halite) and anhydrite and forms beds and lenses
interstratified with limestone, shale, and clay, especially in rocks of Permian
to Triassic age. Gypsum also occurs in volcanic fumarolic deposits and as
an accessory mineral in metalliferous veins.
(ha'-bit) The characteristic shape of a mineral, either the shape of an
individual crystal or the shape and style of
of the same mineral species.
Abbreviation for hydrochloric acid.
hydrothermal (hy-dro-ther-mal) Of or pertaining to hot
water, to the action of hot water, or to the
products of this action, such as a mineral deposit precipitated from a hot
aqueous solution, with or without demonstrable association with igneous
processes; also, said of the solution itself.
deposit (hy-dro-ther-mal de-pos-it) A mineral deposit
that formed through the crystallization of minerals from the hot, ascending
aqueous solutions typically but not always derived from or heated by a magma.
hydrothermal solution (hy-dro-ther-mal so-lu-tion)
Heated or hot magmatic emanations rich in water as well as heated aqueous
solutions that are not demonstratively produced by or related to igneous magmas
or activity. Acidic or salt-carrying hydrothermal solutions are capable of
dissolving silicate and ore minerals and carrying the dissolved metals and ions
hypothesis (hy-poth'-e-sis) A formulation of a
natural principle based on inference from observed data that is tentatively
assumed, and then tested for validity by comparison with observed facts and by
experimentation. A theory is less firmly founded and accepted by the
scientific community than a theory. Once a hypothesis has been tested and
is generally accepted by the scientific community, it becomes a
Color is inherent and due to some aspect of the chemical composition and crystal
structure. Idiochromatic is the opposite of allochromatic.
igneous (ig'-ne-ous) A rock or mineral that formed through
the crystallization or solidified of molten or partly molten magma (molten
rock). Igneous is applied to processes leading to, related to, or
resulting from the formation of such rocks. Igneous rocks are one of the
three main classes of rocks, the others being metamorphic and sedimentary.
index of refraction (in'-dex of re-frac'-tion)
The ratio of the velocity of light in a vacuum to the velocity of light within a
substance. The index of refraction is a function of temperature, pressure
and wavelength of light. Birefringent substances, that is, all substances
that are anisotropic, have more
than one index of refraction.
Isometric minerals and amorphous
mineraloids are isotropic, that
is, their properties are the same in all directions. All other minerals
and materials have optical properties that vary with
induration (in'-dur-a-tion) The hardening or
lithifiation of a rock or rock material by heat, pressure, or the introduction
of cementing material, especially the process by which relatively consolidated
rock is made harder or more compact.
inorganic (in-or-gan'-ic) Any chemical compound that
does not contain the element carbon, with the exception of carbon dioxide, and
compounds containing a carbonate radical (i.e. carbonate minerals with the CO3
(i'-on) An atom or
radical that has lost or gained one
or more electrons, and thus
acquired an electric charge. Cations are positively charged
ions. Anions are negatively charged ions.
A group of islands located on an oceanic plate that have a curving, arc-shaped
pattern of distribution. The islands in an island arc are the result of
convergent plate volcanism over a subduction zone.
isometric (i'-so-me-tric) The crystal system
characterized by three orthogonal axes of equal length. Also known as
isotope (i'-so-tope) An atom of any particular element that has
the same number of protons but differing numbers of neutrons in their nucleus.
Carbon isotopes, for example, all have six protons in their nuclei, but
carbon-12 has six neutrons, carbon-13 has seven neutrons, and carbon-14 has
A dense, compact, black, low-grade coal or lignite that can be polished to a
(la'-va) An extrusive volcanic rock with sufficiently low
viscosity that it can flow under the influence of gravity.
limestone (lime'-stone) A
sedimentary rock consisting
primarily of the mineral calcite
(hexagonal CaCO3) with or without some magnesium carbonate (MgCO3)
or dolomite (CaMg(CO3)2).
Limestone is the most widely distributed of the
carbonate rocks, and is the
consolidated equivalent of limy
mud, calcareous sand, and/or
shell fragments. Clay minerals, quartz, and chalcedony are common
The process by which a newly deposited, unconsolidated sediment is changed into
a coherent, solid rock through cementation, compaction, desiccation, and
crystallization. Lithification may occur concurrent with, soon after, or
long after deposition.
lithosphere (lith'-o-sphere) In plate tectonics, the
solid outer layer of the Earth that deforms brittlely relative to the underlying
ductilely-deforming asthenosphere. The lithosphere includes the
crust and part of the upper mantle and ranges in thickness from less than 1 km
at the oceanic spreading ridges to about 100 km in mountainous continental
(lus'-ter) The way in which a mineral reflects light from its surface.
Luster is a function of the smoothness of the mineral surface and its
reflectivity. Categories of luster include metallic, submetallic, and
within nonmetallic; vitreous, adamantine, pearly, earthy, and dull.
(mag'-ma) Naturally occurring molten rock, generated within the
Earth and capable of intrusion and extrusion, from which igneous rocks are
derived through solidification and related crystallization processes.
Magma may or may not contain suspended solids (such as crystals and rock
fragments) and/or gas phases.
metamorphic (met'-a-mor-phic) A preexisting rock or mineral
that undergoes mineralogical, chemical, and/or structural changes while in the
solid state in response to marked changes in temperature, pressure, shearing
stress, and chemical environment. This generally occurs at depth in the
Earth's crust during contact metamorphism, continental collision or subduction.
Metamorphic rocks are one of the three main classes of rocks, the others being
igneous and sedimentary.
meteoric water (me-te-or'-ic wa'-ter))
Ground water of atmospheric origin. Meteoric water reaches the Earth's
surface as precipitation (rain, snow, hail, or sleet).
mineral (min'-er-al) A naturally occurring, usually
inorganic, solid homogenous material with a definite chemical composition
variable within fixed limits and a highly ordered atomic arrangement. For
a detailed explanation, see Just
What Is a Mineral.
mineraloid (min'-er-al-oid) A naturally occurring,
usually inorganic solid that is not considered to be a
mineral because it is amorphous,
that is, it lacks a long-range three dimensional ordering of its structure.
Mohs scale A standard represented by ten mineral of varying
hardnesses by which the hardness of other minerals may be rated. From
softest to hardest (numbered one to ten), the scale includes:
mollusc (mol'-lusc) A solitary
invertebrate belonging to the
phylum Mollusca, characterized by a nonsegmented body that is bilaterally
symmetrical, and by a radially or biradially
symmetrical mantle and shell. Among the classes included in the
molluscs are the gastropods (snails), bivalves (pelecypods), and cephalopods
(squid, nautiluses, ammonites, and octopi).
muscovite NEED A DEFINITION.
neutron (neu'-tron) A fundamental particle of matter
having almost the same mass as the proton,
but without an electric charge. It is a constituent of the nucleus of all
elements except hydrogen. See atom.
obsidian (ob-sid'-i-an) A black or dark-colored
volcanic glass, usually of
rhyolitic composition, characterized by
conchoidal (shell-shaped) fracture, produced by quick cooling of lava on or near
the Earth's surface.
(o'-pal) A transparent to nearly opaque mineral or
consisting of packed spheres of silica and interstitial (i.e.: filling the
spaces between the spheres) water (typically 3 to 9%). Opal may have a
marked play of colors in the case of precious opal, or opalescence
(more of a diffuse glow) in the case of common opal.
(o'-phi-o-lite) A stratigraphic section consisting of a suite of mafic and
ultramafic igneous rocks and associated marine sediments and their metamorphic
equivalents representing the oceanic crust and upper part of the mantle formed
either at a oceanic spreading ridge or in a back arc basin behind a island arc.
A complete section consists of a basal peridotite representing the upper layer
of oceanic mantle, layered ultramafic and mafic igneous rocks ranging in
composition from peridotite through gabbro, a dike complex consisting of steeply
inclined basic feeder dikes, basaltic lavas and pillow lavas (formed by
submarine eruption of basaltic lavas), capped by a layer of chalcedony and other
marine sediments. This sequence of rocks is typically extensively altered
to serpentine and other secondary minerals, and strongly tectonically deformed.
(op'-ti-cal prop'-er-ties) A subset of the physical properties of a
mineral that are a function of the interaction of light with mineral composition
and atomic structure. These properties include color, luster, index of
refraction, dispersion, pleochroism, play of color, luminescence, and
fluorescence. For more information on this topic, see
Science of Minerals.
organic (or-gan'-ic) Containing carbon compounds and
produced by living organisms.
orthoclase NEED A DEFINITION.
orthorhombic NEED A DEFINITION.
oxidation state (ox-i-da'-tion state)
(equivalent to valence) The
number of electrons that must be added to or subtracted from an
atom during chemical bonding to convert
it to the elemental form. The oxidation states of iron (Fe) and oxygen (O)
in the mineral hematite (Fe2O3) are +3 and
+2, respectively. The formula of the mineral magnetite is usually
written Fe3O4, but it is more informative to write Fe3+(Fe2+,
Fe3+)2O4 to indicate that iron in
magnetite occurs in two oxidation states. Many elements, especially the
other transition metals, are similar to iron in that they have multiple
oxidation states. For instance, the element vanadium (V) occurs in four
oxidation states: +2, +3, +4, and +5.
A dense, variously colored, and usually lustrous concretion formed of concentric
layers of nacre (nacre is 82-86%
orthorhombic calcium carbonate (CaCO3) in a cryptocrystalline
(microcrystalline) aggregate, 10-14% organic material, and 2% water).
Pearls occur as abnormal growths around sand grains or other irritants within
the shell of some molluscs. They are used as gems.
pegmatite (peg'-ma-tite) A typically coarse-grained igneous
rock formed through the crystallization of the very-last stages of
magma typically granitic in
composition that is enriched in water and other volatile elements (F, Cl) and,
in some cases, highly incompatible elements (lithium, beryllium, boron,
fluorine, niobium, tantalum, uranium, and the rare earth elements) that do not
fit into the structures of minerals crystallized at higher temperatures and
pressures. Although most pegmatites are composed of the common minerals
biotite, pegmatites rich in
incompatible elements may also contain rare minerals. These incompatible
elements make up a tiny fraction of the original magma, but because they are
concentrated in the water-rich residual melt, they can occur in large enough
quantities to produce large, well-formed crystals of beryl, chrysoberyl and
euclase (beryllium), tourmaline (boron), topaz (fluorine), apatite (chlorine and
fluorine), spodumene and lepidolite or lithium-rich pyroxene and mica, monazite
(rare earth elements), tantalite (tantalum), and columbite (niobium).
periodic table of the elements A listing of all known
chemical elements by their atomic
number and chemical behavior. A
is provided by the Los Alamos National Laboratory CST Division.
petroleum (pe-tro'-le-um) A naturally occurring complex
liquid hydrocarbon, that after distillation and removal of impurities, yields a
range of combustible fuels, petrochemicals, and lubricants.
physical properties (phys'-i-cal
prop'-er-ties) The characteristics of a mineral that are a direct result
of their chemical composition and atomic structure, and that can be used to
determine the identity of the mineral, including but not limited to crystal form
and habit, cleavage, fracture, density, tenacity, color and streak (color of
powdered mineral), luster, and magnetism.
piezolectric (pie-zo-lec-tric) Capable of producing a
surface electric charge when deformed elastically. Only minerals that lack
a center of symmetry may have this property.
play of colors A flash of colors
produced in a mineral such as precious opal when it is viewed from
different angles. This phenomenon is due to optical diffraction.
pleochroism (ple'-o-chro-sim) The phenomenon in which
the color of a mineral varies or changes with orientation.
An aggregate of crystals of the same mineral species.
A chemical composition that can occur in more than one atomic or mineral
structure. Graphite and diamond (C), calcite and aragonite (CaCO3),
andalusite and sillimanite and kyanite (Al2SiO5), low
quartz, high quartz, cristobalite, tridymite, coesite, and stishovite (SiO2)
are all examples of polymorphs.
porphyry (por'-phyry) An
igneous rock that contains larger crystals in a fine-grained groundmass or
matrix typically indicating at least two rates of cooling and crystallization.
porphyry copper deposit
(por'-phyry cop'-per de-pos'-it) A large body of rock, typically a
porphyry (an igneous rocks that contains larger crystals in a fine-grained
groundmass or matrix), that contains disseminated chalcopyrite and other sulfide
minerals. Such deposits are mined in bulk on a large scale, generally in open
pits, for copper and byproduct molybdenum. Most deposits are 3 to 8 km across,
and of low grade (less than 1% Cu). They are always associated with intermediate
to felsic hypabyssal porphyritic intrusive rocks. Distribution of sulfide
minerals changes outward from dissemination to veinlets and veins. Supergene
enrichment has been very important at most deposits, as without it the grade
would be too low to permit mining.
deposit (por'-phyry de-pos'-it) A deposit in which
minerals of copper, molybdenum, gold, or less commonly tungsten and tin, are
disseminated or occur in a number of small veinlets within a large mass of
hydrothermally altered igneous rock. The host rock is commonly an intrusive
porphyry, but other rocks intruded by a porphyry can also be hosts for ore
(pro'-ton) A fundamental particle of matter, having a mass of 1.67 x 10-24
gram and a positive electric charge. Its mass is almost the same as that
of a neutron, and 1837 times that of
an electron. Protons are
constituents of all atomic nuclei, their number in each nucleus being the atomic
number of the element (from 1 in hydrogen to 106 unihexium, through elements 116
and 118 discovered by particle physicists in 1999).
pyroelectric (py'-ro-e-lec-tric) Capable of producing
a surface electric charge when temperature changes. Only minerals that
lack a center of symmetry have this property.
(quartz) A hexagonal mineral composed of SiO2 and
polymorphous with tridymite, cristobalite, coesite, stishovite, and
keatite. There are many varieties of quartz. Amethyst is purple
quartz resulting from the oxidation of Fe+3 to Fe+4 by
irradiation by gamma rays. Aventurine is a quartz that includes tiny plates of
mica, hemitite, or other minerals. False topaz or citrine is a yellow
quartz. Rock crystal is a watery clear variety. Rose quartz is a
pink variety. Rutilated quartz contains needles of rutile. Smoky quartz is
a brownish variety, sometimes called cairngorm. Tigereye is crocidolite
(an asbestisform mineral) replaced by quartz and iron oxide and having a
rare earth elements
A family of elements, consisting of scandium (atomic number 21), yttrium (atomic
number 39), and the elements in the Lanthanides series, that chemically behave
in similar ways because of the similarity in atomic structure, atomic radii and
valances (3+ or 4+). Lanthanum, (atomic number 57),
cerium, praseodymium, niodymium, promethium, samarium, europium, gadolinium,
terbium, dysprosium, holmium, erbium, thulium, ytterbium, through lutetium
(atomic number 71) are the elements in the lanthanide series.
radical (rad'-i-cal) Negatively charged polyatomic
(multiple) ions or molecular groups
of ions that occur in many compounds, and which remain unchanged through
chemical reactions. Examples are the borate (BO3)-3,
carbonate (CO3)-2, sulfate (SO4)-2,
and hydroxyl radicals
refraction (re'-frac-tion) The bending of light as it
moves between materials with different indices of refraction.
refractive index A mathematical
constant equal to the ratio of the velocity of light in a vacuum (which is
approximately equal to the velocityof light in air) to that in a substance or
mineral. The refractive index determines the angle at which light bends
when it enters a substance at and oblique angle.
rhombohedral NEED A DEFINITION.
A well-consolidated or lithified assemblage of grains of one or more minerals.
Rocks are formed through igneous including hydrothermal, sedimentary, or
rhyolite (rhy'-o-lite) A fine-grained extrusive
volcanic rock that has a composition roughly equivalent to the intrusive
coarsely crystalline granite. A group of extrusive igneous rocks,
typically porphyritic (containing two or more sizes of crystals) and commonly
exhibiting flow texture, with phenocrysts (large crystals) of quartz and alkali
feldspar in a glassy to cryptocrystalline groundmass. Most rhyolites form
through the accumulation and compaction of volcanic material explosively ejected
in a volcanic explosion. Volcanic rocks formed in this manner whatever the
composition are called tuffs or pyroclastic rocks. Rhyolites very rarely
make up extensive lava flows. The extremely high silica content of a
rhyolite magma results in very high viscosity that is resistant to flow.
A strongly foliated (thinly layered) crystalline rock, formed through dynamic
metamorphism, that has a well
developed parallelism of the constituent minerals especially the micaceous or
sedimentary (sedimentary) A rock resulting from the
consolidation of loose sediment that has accumulated in layers, a clastic rock
(such as conglomerate, breccia, or tillite) consisting of mechanically
formed fragments of older rock transported from its source and deposited in
water or from air or ice, or a chemical rock (such as rock salt or gypsum)
formed by precipitation from evaporating sea water, or an organic rock (such as
certain limestones) consisting of the remains or secretions of plants and
animals. Sedimentary rocks are one of the three main classes of
rocks, the others being igneous and metamorphic.
A fine-grained, detrital,
sedimentary rock, formed by the
lithification of clay, silt,
or mud. It has a finely laminated (composed of layers) structure, that
gives it a fissility, or tendency to split along bedding planes. Shale is
well indurated, but not as hard
as argillite or slate.
siliceous NEED A DEFINITION.
(skarn) A metamorphic rock composed of silicate minerals produced through
the metasomatic replacement of carbonate rocks (typically) in a the contact
metamorphic aureole of an igneous intrusion. The silicate rocks are
produced through the metasomatic reaction of carbonate minerals and elements
derived from or mobilized by the magma that typically is of intermediate
specific gravity (spe-cif'-ic
grav'-i-ty) A measure of density, equivalent to the ratio of the weight of
a given volume of a substance to the weight of an equal volume of water.
subduction (sub-duc'-tion) The process of one oceanic
lithospheric plate descending beneath another (usually continental) lithospheric
sulfide (sul'-fide) A mineral compound formed through
the binding of sulfur and a metal, such as iron in pyrite (FeS), copper and iron
in chalcopyrite (CuFeS2), and lead in galena (PbS).
(sul'-fur) An orthorhombic,
nonmetallic mineral composed of the element sulfur (S). Much of the sulfur
formed at or near the Earth's surface is produced by bacteria. Sulfur also
crystallizes from magmas and around
volcanic vents, from fumaroles (heated, sulfur-rich waters derived from magmatic
activity), and hot springs.
An ore enrichment process occurring near the Earth's surface typically produced
by descending meteoric waters containing metal ions in solution.
supergene enrichment (su-per-gene
en-rich-ment) A mineral deposition process in which near-surface oxidation
of ore minerals produces acidic solutions that leach metals, carry them
downward, and reprecipitate them, resulting in the enrichment of sulfide
minerals already present.
symmetry (sym'-me-try) The correspondence in shape or
length of elements in a crystal, such as similar crystal faces, that indicates
the ordered internal arrangement of a crystalline substance, as though repeated
by a mirror, rotation about an axis, or inversion through a point (center of
NEED A DEFINITION.
(teph-ra) The general term for airborne volcanic ejecta of any size.
Fragmental volcanic products between 0.25 cm to 6.35 cm (0.1 to 2.5 inches) in
diameter are called lapilli. Material finer than 0.1 inch is called ash.
Fragments larger than about 6.35 cm (2.5 inches) are called blocks if they were
ejected as solids, and volcanic bombs if ejected as liquid or semi-solid lava.
In a major explosive eruption, most of the pyroclastic debris would consist of
lapilli and ash. Volcanic bombs are aerodynamically shaped by their
passage through the atmosphere. Cinders or scoria are lapilli- or
bomb-size irregular fragments of lava containing abundarnt vesicles or gas
cavities. Pumice is a low density cinder riddled with gas vesicles that is
light enough to float on water.
(the'-o-ry) A scientifically accepted general principle or body of
principles offered to explain natural phenomena that is consistent with
evidence, data, and experimental results. Theories can be disproved, but
it is scientifically impossible to prove a theory correct.
NEED A DEFINITION.
transition element or metal (trans-si'-tion
el'-e-ment) Any of a number of elements than can form bonds with the
electrons from the outer two shells. The transitions elements are
all metals and that most of them are hard, strong, and lustrous, have high
melting and boiling points, and are good conductors of heat and electricity.
Most of these elements have multiple
oxidation states. The
transition elements include elements with
atomic numbers 21 through 30 (scandium through zinc), 39 through 47
(yttrium through silver), 57 through 79 (lanthanum through gold) and occupy the
middle portions of the long periods of the periodic table of elements in groups
3 through 12. Transition elements that are common in minerals, or occur in
significant amounts, are titanium, chromium, manganese, iron, cobalt, nickel,
copper, molybdenum, silver, tungsten, gold, platinum, and mercury.
Yttrium, zirconium, niobium, lanthanum, hafnium, rhenium, and osmium are
important industrially in semiconductors or for geologic dating.
(tuff) A volcanic rock formed through the consolidation of pyroclastic
fragments. Tuffs are extrusive volcanic rocks that form through the
accumulation and compaction of volcanic material ejected during a explosive
volcanic eruption. Most of this material consists of volcanic ash and glass
A rational intergrowth of two or more single crystals of the same mineral in a
mathematically describable manner. The
symmetry of the two parts may be reflected about a common plane, axis
valence (va-lence) (equivalent to
oxidation state) An
integer (whole number) that represents the power of one
element to combine with another.
For example, if hydrogen (H) and chlorine (Cl) both have a valence of 1, oxygen
(O) -2 and nitrogen (N) +3, the valence-balancing
principle gives the formulas HCl (hydrogen chloride or hydrochloric acid), H2O
(water), NH3 (ammonia), and HNO3 (nitric acid).
The subscript numbers indicate the relative numbers of
atoms of each element. Many
elements have multiple valences; for
example, the element vanadium (V) occurs in
four valences, +2, +3, +4, and +5,
and iron (Fe) occurs in two valences, +2 and +3.
(vol-ca'-no) A conical hill, low rounded mound, or rugged steep-sided
mountain built around a vent that connects with reservoirs of molten rock below
the surface of the Earth. The term volcano also refers to the opening or
vent through which the molten rock and associated gases are expelled.
Volcanoes are composed of any of the following volcanic materials: lava (molten
rock erupted on the Earth's surface), tephra
(airborne volcanic material of any size including ash, lapilli, and volcanic
bombs), cinders or scoria (lapilli- or bomb-size irregular fragments of lava
containing abundarnt vesicles or gas cavities). Pumice is a low density cinder
riddled with gas vesicles that is light enough to float on water.
volcanic NEED A DEFINITION.