Absorption Spectrum....Colors of light least absorbed
combining to produce the color of the stone. The stone,
when viewed by spectroscope, will show as dark bands
in characteristic positions the colors most strongly
absorbed.
Acicular...Needlelike; refers to the growth of a mineral in long and slender crystals.
Adamantine... Very high luster.
Aggregate...Intergrowth of several crystals, these may be globular, fibrous, reniform, or radiating fibrous.
Adularescence...The sheen of color seen in moonstone and other feldspars of the adularia variety.
Allochromatic Minerals...Minerals that are colorless when
pure, the color coming from coloring agents, most of
which are, cobalt, copper, chromium, titanium, vanadium,
manganese, and iron. Examples of this are beryl,corundum,
quartz, and spinel.
Alluvium...Continental sediments due to transport and
deposition of gravel, sand, and clay by running water,
rivers, and streams. (See alluvial)
Alpha rays...Helium atoms with double positive charge.
Alpine cavities (vugs)...Hollows in silicate rock, they may be partially filled with mineral formations.
Alteration pseudomorph...One mineral has been replaced by
another that is unrelated while preserving the original
crystal form.
Amorphous...Has no characteristic external form or shape. The arrangement of the atoms and molecules are irregular
Amphiboles...A group of closely related, dark colored rock forming silicate minerals, as in, actinolite, hornblende.
Anisotropic... when applied to crystals it is the display of unequal physical properties in different directions. An example would be a mineral which has a different hardness when tested in different directions.
Amygdaloidal...(amygdule) gas filled volcanic rock.
Amygdule...A rounded mass of mineral formed in a gas cavity.
Angstrom Unit...Unit and length of measurement of wavelengths
of visible light and most xrays. (1 A.= .0000001
millimeter)
Anisotropic...Crystals in which the optical properties
vary with direction. All crystals except those in the
cubic system are in this category, and exhibit double
refraction.
Aphanitic rock... That rock in which the crystals are too small to be seen by the unaided eye.
Arid... dry or desert like.
Arsenates...Minerals in which AsO4 radical is an important constituent.
Asterism...Stones containing suitably oriented rod like inclusions or channels, that are cut as cabochon in the correct direction show this star effect. Star effect.
Atom...The smallest part of a chemical element which remains unchanged during all chemical reactions.
Atomic Weight...Weight of an atom compared with an atom of oxygen (16.00).
Batholith... A huge body of plutonic rock that has been
intruded deep into the earth's crust and latter exposed by
erosion.
Bean (pisolitic) iron ore... Globular aggregates of limonite
that occur in karst cavities as weathering formations.
Beta rays...Electron rays
Bezel... A rim of metal surrounding a gemstone securing it.
Biaxial...Two optic axes or double refraction. Usually
crystals in the rhombic, monoclinic, and triclinic system.
Bipyramid (dipyramid)...Crystals that form symmetrically
about a plane dividing it into two pyramids.
Birefringence...Same as double refraction. Splits rays of
light passing through a transparent object as glass or
crystal.
Botryoidal... Resembling a bunch of grapes in rounded masses
of a mineral.
Boule...The form and shape of a synthetic stone when created
by the inverted blowpipe of a Verneuil furnace, somewhat
carrot shaped.
Breccia...An aggregate of angular fragments of stone or
mineral cemented together as in calcite and chalcedony.
Brilliant...The cut of a gemstone that is round and has 32
facets plus the table above the girdle, (crown), and 24
facets plus any culet below the girdle, (pavilion).
Cabochon...The cut of a gemstone that has a convex surface.
A cab.
Cameo... A carved shell, sometimes cut from onyx or other
mineral containing bands of different colors, To cut in
relief, the opposite of intaglio.
Carat...Unit of weight used to weigh gemstones, equal to 200
milligrams, or .200 grams. 1 gr. = 5 ct. 100 points = 1 ct.
metric system.
Cataclastic rock... A metamorphic rock produced by the
crushing and grinding of preexisting rocks, which are still
visible as crushed fragments.
Chatoyancy...Cat's eye effect produced by some gemstones
when cut properly in cabochon. See asterism.
Chelsea Filter...A dichromatic color filter transmitting
light of only two wavelengths, one deep red the other
yellow green. Used to discriminate between emerald and
synth. spinel and green glass colored with cobalt.
Chemical Element...Matter composed of atoms of only one
chemical type which cannot be decomposed into simpler
substances by chemical methods.
Clastic rock... Sedimentary rock made up of fragments of
preexisting rocks and transported into the place of
deposition.
Cleavage...The tendency of stones to split along one or more
definite directions, always parallel to a possible crystal
face.
Conchoidal..(fracture), A breakage which leaves a conchoidal
shell shaped surface.
Conglomerate ( as in geology) .. Conglomerates, as well as
sedimentary breccias, are coarse-grained SEDIMENTARY ROCKS
formed by the consolidation and hardening of, respectively,
rounded and angular gravel deposited in oceans. More than
30 percent of the large particles of these rocks exceed 2
mm (0.08 in) in diameter. The particles may be pebbles,
cobbles, or boulders, or mixtures of these sizes. Both
conglomerates and sedimentary breccias may be named and
classified by the proportion of gravel - sized particles;
the type of matrix,and the types of gravel-sized particles.
The proportion of gravel is a function of the highest
current speed at the time of deposition and the
availability of particles of such coarse size. A sample
that is more than 80 percent pebbles, cobbles, or boulders
is called a conglomerate proper, whereas one that is 30 to
80 percent is an arenaceous (sandy) conglomerate or an
argillaceous (shaley) conglomerate. The matrix between the
layers of coarse particles may also be calcareous (that is,
containing calcium carbonate) or sideritic (containing
ferrous carbonate). On the basis of the variety of pebbles,
cobbles, and boulders in conglomerates, they can be
classified as oligomictic, consisting of a single kind of
rock (such as one of various varieties of chert and
quartzite or other rock), or polymictic, containing many
kinds of rock.
Concretion...Knobby or rounded mineral concentrations in
sedimentary rocks that are completely surrounded by rock.
Contact metamorphism...The change of rock due to the effect
of high temperatures during contact with a lava flow, magma
sloping, or igneous intrusion.
Critical Angle...The angle at which a ray of light passes
from one medium to another, as a gemstone and air.
Cryptocrystalline.......The structure of a substance as
chalcedony, that consist of very small crystals but show no
external sign of crystal structure.
Crystal..A homogeneous body in the form of a geometric solid
bonded by polyhedral faces, the nature of which is
expression of the orderly and periodic arrangement of its
constituent atoms.
Crystal Axes..."Lines" passing through a crystal in
important symmetric directions, intersecting at the
center of the crystal.
Crystal Systems...The six main groups into which
crystals can be classified: triclinic, monoclinic, orthorhombic, cubic, tetragonal and hexagonal.
Decrepitation... The explosive shattering of mineral grains on
heating.
Dendrites... Skeletal crystals that develop from
supersaturated solutions, often in small cracks, often
resembling plant or trees.
Density...The ratio of the weight of a substance to its
volume expressed in g/cm 3, and numerically equal to the
specific gravity.
Detrital...Occurrence of minerals in gravels that came from a
mineral deposit. (placer)
Diaphaneity...Showing light through its substance;
transparent; translucent.
Dichroism...Possessing the property of showing two different
colors when viewed from different angles.
Dike... In the forming of rocks, when intruding sedimentary
rocks in a vertical or nearly vertical position.
Dispersion..The separation of white light into its
constituent colors by its refraction or diffraction.
Double Refraction...Ability of certain crystals to split
incident light into two rays with different refractive
indices.
Doublets...A common method of building up sufficient
thickness to permit a gem to be used in a setting. A
non gem mineral is cemented to the top or bottom of the
gem material. (See Opals.)
Dripstone...stalagmites or stalactites
Druse...A crystal coated surface of rock.
Doctile...Able to be drawn into a wire.
Endogenous...Generated deep in the earth by volcanism or
earthquakes.
Enhydro...A chalcedony or carnelian geode having the
center cavity filled with water.
Epithermal vein... Formed at shallow depths from ascending
hot solutions.
Epizone...In regional metamorphism, the depth level nearest
the surface to approx. 3.75 to 4.25 miles.
Extinction...Diminution in the intensity of radiation
due to absorption by or scattering in the medium;
also the stopping of incident X-rays by the outer
layers of atoms in a crystal.
Extraordinary Ray...Crystals and minerals belonging to
the hexagonal tetragonal systems in which the ray or
refractive index varies according to its direction
through the crystal.
Extrusive rock...Igneous rock that solidifies on the surface
of the earth.
Facet...Man made flat part of a mineral, a planar surface.
Ferromagnetism...magnetic even in the absence of an external
magnetic field.
Fire...Same as dispersion
Fluorescence...Temporary emission of radiations of
different wavelength (color) by a substance struck
by light waves usually long or short wave ultraviolet
light.
Fluvial...Deposits from rivers.
Foliated...Made up of thin leaves, like mica.
Formulas...For weight estimation based on measurements
in millimeters to 1/10. assuming well cut stones with
little or no bulge factor.
Some formulas for various gem cuts.
Fracture...A break with an uneven or irregular surface.
Fraunhofer Lines...A series of groups of dark lines in
the spectrum of an object, visible using a spectroscope.
Friable... Easily crumbled or pulverized.
Fumaroles...Spots in or near active volcanos where gases
are expelled.
Gabgue...The minerals of no value in veins with ore
minerals.
Gamma rays...Short wave electromagnetic waves.
Gangue...Minerals of no value associated in veins with
ore minerals.
Geniculated... Knee like intergrowths of crystals.
Geode...A stone having a cavity lined with crystals;
the cavity in such a stone.
Girdle...The wide part of a cut gemstone
Gliding plane... acrystal direction along which the
atoms can slip a defined distance without destroying
the coherence of the crystal.
Grain...(Troy system)..480 grains to the oz.
Habit...Characteristic crystal form.
Hacklt...A fracture characteristic of metals in rock,
like gold and copper. (hackly)
Hardness...The resistance by a substance to actions
which tend to modify its surface by scratching,
abrasion, penetration.
Hemimorphic...Half formed crystals in which the
faces that grow on one end are different in angle
and position from the faces to be found on the other
end.
Hydrothermal...Hot water or solution sometimes superheated
Idiochromatic...Minerals...in which the color is due
to an essential constituent.
Igneous rock.. Rock formed by the solidification of magma.
Inclusions...Substances within a mineral, example, other minerals,
gas bubbles, liquids, or other foreign objects.
Imitation Stones...Substances used to look like
a genuine. ie: glass, plastic, etc.
Inclusions...Solid, gaseous, or liquid material of
various types incorporated in a crystal during its
formation and growth.
Intaglio...Incised carving; a sunken design, ie:
cameo
Intarsia...Mosaic inlay work using colored stones.
(and wood)
Ion...Electrically charged atom, radical or molecule.
Isomorphous ...Minerals in which two or more elements
can replace each other to any extent without notably
changing the appearance of the crystal.
Isotropic...Materials in which the optical character
is the same in all directions.
Labradorescence...Patchy or diffuse iridescence due
to the interference of light by reflection from
parallel inclusions. Example Labradorite.
Light...Radiant energy which gives the sensation
of sight. Velocity is 186,285 miles per second.
Litmus paper... colored paper used to show whether a
solution is acid or alkaline.
Lopolith.. A large, lenticular, sunken mass of igneous rock
whose surfaces are concordant with the enclosing rocks.
Luster...A reflective property of mineral surfaces.
Magma...Molten silica containing volatile substances in
solution, present beneath the surface in certain areas
of the earth's crust.
Malleable...Can be flattened by pounding, as in metals.
Mammillary... rounded mineral surface
Massive...Minerals not bounded by crystal faces.
Metamorphism...(geological)..Changes in rocks brought
about by heat and pressure acting in the rocks just
below the surface.
Meteorite...Solid object that comes from outer space and
falls to earth.
Miaroles...Small cavities in granitic rocks created by
volatile components.
Miller indices...Group of three digits used to designate
crystal faces.
Mohs Scale...The relative scale of the hardness of
minerals, from 1 to 10, the order of hardness with
no significance to quantitative relationship.
Molecule...Two or more atoms in close relationship,
The smallest quantity of an element or compound
which is capable of independent existence.
Monochromatic Light...Light of one wavelength only.
Nicol Prism...Prism for producing polarized light,
having split the light into two rays.
Nodule...A lump or node.
Opaque...Not transparent or translucent. (you can't see
through it)
Optic Axis...The direction of single refraction in a
double refractive mineral.
Optic sign...If the lower index of the refractive reading
does not vary when the gemstone is rotated, it is
uniaxial and + optic sign, if the higher index is
steady and the lower index varies the optical sign
is -.
Ore... A mineral occurring in sufficient amounts to permit
its recovery at a profit.
Organic...compounds of carbon, ie: coal, jet
Orient...Characteristic sheen and iridescence, as
displayed in a good pearl.
Orientation... Applied to crystals, this means
visualizing the disposition of the principal
directions within the crystal.
Orogenesis...A complex phenomena that leads to the formation
of mountain ranges.
Outcrop...Where the bed rock is exposed.
Paleontology... a division of geology that concerns
itself with prehistoric life.
Paragenesis..The sequence in time in which a mineral
crystallizes with respect to the other minerals.
Paramorph...A chemically identical crystal compared with
the original, but the atoms have been rearranged so
that they no longer conform to the original outline.
Parting...A smooth fracture that looks like a cleavage
plane but takes place only on certain planes in the
crystal, not between any set of atoms, like true cleavage.
Paste...Lead glass imitation stone.
Pegmatites.....A very coarse platonic rock, generally
granitic in composition. Usually forming dikes
that cut granite or the gneisses and schists
that border granite masses. They are coarse because
the liquid residue at the time of their crystallization
contained a high percentage of water and other volatile
elements that did not go into the makeup of the common
minerals of granite, and were concentrated in the residue.
Petrography.. The branch of geology that deals with the
description and classification of rocks.
Phaneritic rock.. An igneous rock in which all of the
essential minerals can be seen by the unaided eye.
Phenocryst...Crystal that is set in a finer grained ground
mass.
Phosphorescence...Luminescence emanating from substances
that have been irradiated with ultraviolet light or
X-rays, but persisting after the source of stimulation
has stopped.
Piezoelectric...A substance that becomes electrically
charged by pressure.
Pipe...In geology, the tubular ascending structures in
volcanic rock.
Placer...Concentrations of heavy or resistant minerals that
have been transported to rivers or other water areas.
Plastics...Synthetic resin, hard, usually molded.
Pleochroism...Dichroism and similar effects shown by
some biaxial minerals in which three distinct colors
or shades can be seen by using a dichroscope. (two at
a time)
Plutonic rock...rock that has solidified deep underground.
Pneumatolysis...The action of gases of a magma on the
surrounding rocks and on the solidifying molten mass
itself.
Point...(diamonds).. 1/100 of a carat, .01 ct.
Polarized Light...Light which vibrates in one direction
or plane.
Polaroid...Class or plastic which passes light on one
plane.
Potch...native material in or around a gemstone, a dead
spot or area. ie: ironstone surrounding opal.
Radioactive...Emitting alpha, beta, or gamma rays.
Reconstructed Stones...Old method of fusing Stones made
from chips. Used now to describe amber remelted and
fused from otherwise unusable pieces.
Reflection...The throwing off or back, light from the
surface.
Refraction...The bending of light passing through one
medium to another. The changing of direction.
Refractive Index...The measurement of the amount of
change in direction of light passing through one
medium to another. The ratio of the velocity of
the light in air to the velocity of light in the
medium being measured.
Refractometer...Instrument used to determine the
refractive index of various substances.
Rock...Stoney matter. Any mass of mineral matter
forming an essential part of the earth's crust.
Sclerometer...Device for the quantitative measuring of
hardness.
Sedimentary Rocks...formed originally of sediment,
including shale and sandstone, composed of
fragments of other rocks deposited after transportation
from their sources, and including those
formed by precipitation, as gypsum, or by calcareous
secretions of animals as in certain limestones.
Selvage...The area bordering a vein.
Sheen...The iridescence of light reflected from
the surface of a stone. ie: moonstone
Silk...Fine rod like crystals embedded in a crystal
Skarn...Contact rock of igneous silicate masses with
limestone.
Specific Gravity...The weight of a substance
compared to the weight of an equal volume of
pure water at 4 degrees C.
Spectroscope...Instrument which resolves light
into its component wavelengths by refraction
through prisms or diffraction grating.
Spectrum...The band of light showing the succession
of rainbow colors corresponding to the different
wavelengths. The VISIBLE spectrum is the small
portion in the vast spectrum of electromagnetic
waves, which extend from very long waves, (now used
by submarines for underwater communication) to very
short waves (gamma) emitted by radioactive elements.
Stalactites...dripstone, stalagmite..the formation of
a conelike structure that grows from the deposits of
carbonate of lime build up.
Star...The effect of proper cutting of a gemstone as
a cabochon when the gemstone contains long rod like
crystals or fibers in parallel or cavities where
these have formally been. The reflection, (using a
single light source), from the surface produces lines
in even numbers, ie: 2,4,6,8,12, with a common center.
Step cut...(trap cut)..Cut with edges are parallel
to those the rectangular table.
Synthetic stones...Man made stones which have
approx. the same composition and or crystal
structure of the natural crystal which they
represent. (See synthetic diamonds.)
Transparency...The degree to which light passes
through a substance.
Twin Crystals...Two or more crystals which have
grown together in a symmetrical fashion.
Ultraviolet Light...Wavelengths of light shorter
than visible violet light.
Ultrabasic rock.. Any plutonic igneous rock with very low
silica content.
Uniaxial...Minerals having single refraction, one
optic axis.
Vacuolar texture .. texture typical of igneous
rocks rich in cavities.
Vectorial properties .. properties of a mineral
which vary with direction.
Vein...A more or less upright sheet deposit of
minerals, cutting other rocks and formed from
solutions rather than from a molten magma as in
a dike.
Vicarious elements .. those that take each other's
place in trace amounts in a mineral,s crystal
structure.
Vitreous.. Glasslike in appearance or texture.
Vug...An open cavity in rocks, often lined with
crystals.
Xenolith .. rock enclosed in magma.
Xrays...Electromagnetic radiations of a shorter
wavelength than visible light. Usually less than
one Angstrom.
The above is extracted from the GEMSTONE program