Terminology

TermDefinition
AbrasiveSubstance used to cut and polish rocks
Often called "grit"
Absolute hardnessScale for measuring the hardness of a mineral
Absorption spectrumSpecific bands of light that pass through and those that get absorbed into a gem and disperse into the colors of the spectrum
Accessory mineralMineral that occurs with other minerals
Acetic Acid(CH3COOH) Dissolves salts, sugars, and oils
Vinegar is acetic acid mixed with water
AcicularAggregate of long, slender crystals
AcidGroup of chemicals containing a free hydrogen element
Acid TestProcedure performed to help identify a mineral by using certain acids (usually hydrochloric and nitric) in contact with a mineral or its powder
ActivatorPart in a fluorescent substance that causes the substance to glow when exposed to ultraviolet light
AdamantineDescribes the luster of transparent minerals that are very brilliant with a bright shine
AditMine entryway
Usually horizontal
AdularescenceOptical effect exhibited on certain minerals where they display a billowy, ghost-like reflection with a bluish-whitish color emanating from the surface
AgateType of microcrystalline (too small to see with the naked eye) quartz called chalcedony
Usually forms in cavities in volcanic rocks
Agate ProbeMetal rod used to detect underground agates
AggregateGroup of mineral crystals
AlkalineChemical substance that is either a hydroxide, carbonate, or metal oxide that has the ability to react with acids to form salts
AlloyMixture of two or more metals or semi-metals in which the atoms of the different metals are intermingled among each other
AlluvialEroded material that gets transported by rivers or streams
Alluvial depositDeposit in a stream or river where alluvial materials collect
AlpineEnvironment in a mountainous region, often referring to granite zones within the Alps of Europe
Alpine CavitySpecific type of cavity within rock in mountainous regions that is created from the geological stretching and bending of rock
AmalgamAlloy of mercury and another metal
AmberGem made from hardened resin of ancient trees
AmethystPale purple to violet (due to iron compounds) variety of crystalline quartz
AmorphousNon-crystalline
Amphibole groupGroup of minerals that contain iron, magnesium, silicon, oxygen, and hydroxyl
Very similar to pyroxenes, but occur in longer, thinner crystals
Amygdaloidal RockVolcanic rock containing numerous gas cavities filled with secondary material (ie., quartz, calcite, chalcedony, zeolite)
AmygduleMineral-filled cavity or vesicle in a volcanic rock
AnhydrousMinerals that contain no water in their chemical structure
AnisotropicLacking consistent hardness on all surfaces
AnticlineFold in rock where the strata protrudes upwards towards the fold
AntimonidesGroup of sulfides that contain one or more true metals combined with antimony
Apatite groupMinerals that are isomorphous hexagonal phosphates
AqueousFormed from precipitating hard water
ArêteNarrow mountain ridge formed between two glacial valleys or cirques
Argonite GroupGroup of minerals belonging to the carbonate group that are isomorphous with one another
Well-known members include Aragonite, Cerussite, and Strontianite
ArgentiferousContaining silver
ArgillaciousComposed mostly of clay
AridDry, desert region
ArsenatesGroup of minerals that are compounds of one or more metallic elements associated with the arsenate radical
Most are heavy and none are hard; usually brittle and occur in small crystals or compact aggregates
ArsenidesGroup of sulfides that contain one or more true metals with arsenic
AsbestosAny of the several fibrous minerals belonging to both the Serpentine group and the Amphibole group
AsterismProperty of reflecting light in star-like patterns of 4, 6, or 12 rays
AsymetricalNot containing perfect symmetry
Atomic StructureArrangement and the type of atoms that exist in a particular structure
AuriferousContaining gold
AutochthonousRock or mineral that formed in the same location where it was found
AventurescenceEffect caused by small inclusions of a mineral with a highly reflective surface which cause it to exhibit a glistening effect when rotates or looked at different points
BandingPresence of color zoning lines, or "bands" in some minerals
BasalType of cleavage exhibited on a horizontal plane of a mineral by way of its base
BasaltIgneous rock
BatholithVery large mass of igneous rock
BauxiteRock ore from which aluminum is refined
Bead TestComplex, scientific test which is conducted to identify a mineral by crushing it and mixing into a borax flux and heated until a glassy bead forms
BeddingLayering of sedimentary rocks
BedrockLayer of solid rock underneath loose material such as soil or sand
BelemniteFossil of an extinct marine creature similar to squid but possessing a hard internal skeleton and lacking tentacles
Biogenic RockRock formed by organic action
BypyramidCrystal shape in form with a plane dividing a crystal into two pyramids base to base
BirefringenceOptical effect commonly known as double refraction
BitumenOrganic, naturally occurring form of petroleum with a tar-like consistency
BladedCrystal habit describing flat, elongated, "knife-like" crystals
BLMBureau of Land Management
BondLink between atoms to form a secure molecule
BoratesGroup of minerals that are compounds of one or more metallic elements combined with the borate radical
BotryoidalFormed into masses of small spherical bulges
BrecciaSedimentary rock made of jagged or angular mineral fragments cemented together
Brilliant CutType of rounded cut used for gemstones to maximize brilliance and fire
AKA round cut
BrittleForm of tenacity which describes a mineral that gets hammered or scratched and results in a fine powder or small crumbs
BronzeCollective term describing any metallic alloy that ranges in color from light yellow to orange
BullionPrecious metal cast in bulk form such as bars, bricks, or ingots
CabochonRock cut so that its top has a smooth domed surface with no facets
CalcareousComposed of calcite or calcium carbonate
CalciteMain mineral in limestone and chalk
Chemical name = calcium carbonate
CameoGem with a design or figure carved out of stone and raised above the background layer
CanyonDeep, narrow valley often formed when a river cuts through rock
CapillaryAggregate composed of tiny, long, and slender (hair like) crystal strands
CaratStandard measure of weight for precious gems and minerals
1ct = 0.006oz = 0.2g
CarbonatesMineral group whose members contain one or more metallic elements plus the carbonate radical
CarbonatiteType of igneous rock mostly of carbonate minerals
Carbon FossilDelicate organic material that falls to the bottom of bodies of water and is trapped there by layers of sediment (i.e. coal, oil, natural gas)
CarboniferousGeological time period that stretches from around 365 - 290 million years ago
CastFossil formed by the filling of a mold
Cast FossilMineral replaces the soft parts of the organic material and all that is left is the hard parts (i.e., ammonite, dinosaur bones)
Cat's-Eye effectSee chatoyancy
CaveNaturally formed opening in the ground that extends beyond the zone of light and is large enough for a person to enter
CavityHollow area in rock that develops because of some form of stress
Cementation ZoneUnderground area where certain elements are concentrated and can combine to form primary minerals
Chemical Sedimentary RockRock that is formed by mineral precipitation
ChertFine-grained, usually dark-colored sedimentary rock of silica-rich composition
ChitinHorny substance that forms the shells of arthropods
ChondriteType of stony meteorite formed mostly on chondrules
Generally composed from pyroxenes and Olivine and contain Iron-nickel
ChondrulesSmall, millimeter sized spherical grains that were once molten and came together in space through gravitational accretion
ChromatesGroup of minerals that are compounds of one or more metallic elements combined with the chromate radical
Usually brightly colored and heavy
Cinder ConeNaturally expelled debris, usually in a conical pile, surrounding the vent of a volcano
CirqueSteep-sided, bowl-shaped hollow in a mountain, carved out by a glacier
ClaimTract of public land staked out to mine
ClastFragment of broken rock
Clastic SedimentSedimentary rock made mainly of broken rock fragments
ClayMineral particles that are smaller than 0.00008" (0.002mm) wide and are common in soil and sediment
CleavageThe way certain minerals break along planes according to the mineral's atomic structure
ClinopinacoidElongated crystal with steep, slanty angle towards its top at the base
ClusterDense agglomeration of crystals
CoalDark gray to black, staining and greasy rock formed by the accumulation and compaction of herbal organic materials
CoatingThin layer of one material on the surface of another
ColumnarLike columns
CompostionElements and quantity of elements a substance contains
CompoundTwo or more elements joined together chemically
Compression FossilFossil preserved in sedimentary rock that has undergone physical compression
ConcentratesMaterial that has been processed and reduced by removing large rocks and organic material
ConcentricForm of banding where the bands are circular, forming rounded or oval-shaped rings around a central point
ConchoidalConcave fracture in a glassy mineral
ConcretionDistinct, hard, compact mass or aggregate of mineral matter that is normally rounded
ConductivityAbility of a substance to act as a conductor of electricity
ConductorSubstance capable of transmitting electricity
Substance that is able to retain heat or pressure
Conflict MineralsMinerals that are mined in war zones to finance terrorist or revolutionary groups
ConglomerateSedimentary rock made up of pieces of rocks that have been worn into rounded shapes and naturally cemented together
ConodontsTeeth of very early fish-like creatures that lived about 515 million - 210 million years ago
Contact Metamorphic RockRock that forms as the heat from magma or a lava flow alters an existing rock
CoproliteFossilized dung
CoralSkeletons of tiny sea animals that live in colonies combined with calcium carbonate into a hard limestone
CoreCenter of the earth, made of heavy metals
~850 miles wide
Country RockRock that surrounds a mineral deposit or igneous intrusion
CoxcombAggregate composed of flaky or tabular crystals that are joined from a base with grooves between long, slender, arc-like crystals
CraterNatural depression marking the vent of a volcano or impact site of a meteorite
CratonAncient part of a continent unaltered for at least 1 billion years
CrazingCondition in Opal or some other gemstones such as Amber that cause them to form internal or surface cracks
CretaceousGeological time period that stretched from about 145-65 millions years ago
CrinoidsLarge class of echinoderms usually have a cup-shaped body with 5 or more feathery arms
CrustThin outer layer of the earth that lies over the mantle
4-45 miles thick
CryptocrystallineRock surface of solid rock that is comprised of extremely minute or microscopic crystals
CrystalGeometric shape which many minerals form
Crystal FormWay in which different faces of crystals are arranged
Crystal HabitTypical shape in which a crystal or cluster of crystals grow
Crystal SystemDifferent groups into which crystals may be placed according to symmetry
CrystallographyScience and study of the formations and mathematics of crystals
CubicShaped as a cube
CuletBottom point of a faceted gem
CutDescription of the type of facet of a gem
CyclosilicatesGroup of silicates that have their tetrahedrons linked into rings
Cymophane EffectPhenomenon seen on a few polished gems and cabochons that cause them to exhibit a floating light reflection that moves as the gem is rotated
Dana NumberNumber assigned to each mineral according to classification system devised by James Dwight Dana
DendritesFern-like growths of crystals lining the cracks and joints in rocks
DepositLay down material such as mud, sand, or gravel in a new location
DesertArid region that typically receives less than 10" on rain each year
Desert RoseNickname for rosette-shaped gypsum concretions and barite formations
DevonianGeological time period that stretches from about 415-360 million years ago
DiatomFossilized microscopic marine plant
DichroicShowing different colors when viewed from different directions
Dike/DykeSheet-like igneous intrusion that is near vertical or cuts across existing rock
DinosaursGroup of extinct prehistoric reptiles that lived 230-65 million years ago
DipDownward angle of inclination of bedrock from the horizontal
DoubletComposite stone made of 2 pieces cemented or glued together
DredgeMining equipment used in streams to suction up material from the streambed to process through a riffle or other device to screen out heavy material (i.e., gold)
DruzyCrust of uniformly tiny crystals filling a cavity or coating a rock
DumpsiteAt a mine site, where the non-economic rocks are deposited
ElectrumNatural mix of gold and silver
ElementMaterial that cannot be broken down into more simple substances by chemical means
EnhydroCrystal that contains a fluid-filled cavity
EoceneEpoch of the Tertiary Period between the Paleocene and Oligocene, about 55-35 million years ago
EpochDivision of geological time, part of a period
EraLargest division of geological time lasting hundreds of millions of years
ErosionWearing away and removal of exposed material by water, wind, and ice
ErraticLarge rock that has been carried by a glacier and dropped from it place of origin
ErosionWearing away of the material on the Earth's surface
EruptionDischarge of lave, pyroclastic material, or gas from a volcanic cone or vent
EvaporiteNatural salt or mineral formed by the process of evaporation
ExfoliationProcess of weathered rock sheets splitting away in layers from larger rock masses
ExposureWhere a rock outcrop is exposed at the surface
Extrusive Igneous RockIgneous rock that forms at the earth's surface
FacetFlat surface on a cut gemstone
FaultLong fracture in rock along which rock masses move
FeldsparMost common, rock-forming minerals, constituting 60% of the earth's crust
FeldspathicRock containing feldspar
FelsicRock rich in feldspar and silica
Fire AgateForm of chalcedony that contains inclusion of iron oxides that result in a play of colors like an opal
Fissure VolcanoVolcano that erupts through a long crack
FloatPieces of rock that have moved from their original source
Flood BasaltPlateau formed from huge eruption of basalt from fissure
FlowstoneGeneral term for the sheet-like mineral deposit on a cave wall or floor
FluorescenceEmission of brightly colored light by a substance when exposed to ultraviolet light rays
FoliationFlat layers of minerals in metamorphic rock formed as minerals recrystallize under pressure
Fool’s GoldPyrite
FormationRelated deposit of rocks formed during the same time period and generally under the same circumstances
FortificationForm of agate with angled concentric banding
FossilRemains, traces, or impressions of organisms that lived millions of years ago and are usually preserved in rocks
Fossil FuelsCoal, oil, and natural gas which are formed from the remains of once-living organisms
FractureWay in which a rock or mineral breaks when it doesn't break along cleavage planes
FulguriteSand fused by lightning
FumaroleHole or vent through which volcanic gases escape
GangueWaste rock in a mineral deposit that is being worked
GastrolithsStones, swallowed by dinosaurs or other animals, used to help grind up food
GemstoneMineral, usually crystalline, that derives particular value from its beauty, color, rarity, and hardness
GeodeRock containing a crystal-lined cavity in which crystals grow toward the center
Geologic Time ChartRecord of divisions of the Earth's history
Geological ColumnDiagram depicting the successive layers of strata that have formed over geologic time
GeologistSomeone who studies the earth
GlacierLarge mass of ice that forms on land and flows slowly downhill under its own weight
Gold DoreBar of gold that is usually about 90% pure
GrainParticle of a mineral
GraphiteMineral made entirely of carbon
GrubstakeSupplies furnished to a prospector in return for a share in discoveries
HabitGeneral shape or appearance of a mineral
Hackly FractureJagged breakage of a metal
HardnessDegree of resistance of a rock or mineral to being scratched
HornSteep-sided mountain peak, formed by erosion by several glaciers
Hydrochloric Acid(HCI) Corrosive acid used mainly for dissolving unwanted substances
Very destructive liquid and will destroy many minerals
Hydrofluoric Acid(HF) Corrosive acid used especially for the production of glass, due to its quality of dissolving the glass
Very destructive liquid and will damage some minerals
HydrothermalWater heated by magma
Hydrothermal Deposit Mineral deposit formed from mineral-rich hydrothermal fluids
Ice AgeUsually referring to the most recent ice age, a portion of the Pleistocene epoch from 1.8 million - 11,000 years ago
IchnofossilsSedimentary structures consisting of a fossilized track, trail, burrow, or tube resulting from the life activities and behavior of an animal
IchnologistScientist who studies fossilized footprints, tracks, and other trace fossils
Igneous RockType of rock that forms as lava or magma cools and hardens
Impact CraterCrater formed by the impact of a meteorite
InclusionPresence of foreign body within a crystal
Index FossilKey fossil used to correlate strata
IntrusionEmplacement of magma into existing rock
Intrusive Igneous RockIgneous rock that forms beneath the surface of the earth
InvertebratesAnimals lacking a backbone or spinal column
IridescencePlay of colors on the surface of a mineral
Island ArcCurved chain of volcanic islands in a subduction zone
JetForm of coal that can be polished to look like black glass
JurassicGeological time period that stretched from 200-145 million years ago
K-T Extinction / Boundary EventApproximately 65 million years ago, at the end of the Cretaceous period when 3/4s of life forms go extinct
"K" refers to Kreide (chalk in German)
"T" refers to Tertiary
KaratParts per 24 of pure gold in an alloy
Karst TopographyGeologic formation shaped by the dissolution of a layer(s) of soluble bedrock
Landscape is characterized by the presence of sinkholes, caves, springs, and underground streams
KimberliteIgneous rocks rich in volatiles, normally forming pipes
KnappingProcess of chipping away at a stone to produce projective points, knives, and other objects
LaccolithMass of intrusive igneous rock with a dome-shaped top and flat base
LapidaryCraftsperson who cuts and polishes gemstones
Last Chance GulchLocation of significant gold rush in Helena, Montana
LavaHot melted rock that flows out of an erupting volcano
Lava TubeHollow formation created when molten lava solidifies on the exterior but the insulation allows the interior to continue to flow and empty creating a hollow tube
LeaveriteRockhounder slang for a rock that isn't worth carrying back home
LithophysaeScientific name for a thunderegg
LithospherePortion of the earth comprising the crust and upper-most portion of the solid mantle
LocateMark the boundaries of a claim
LodestonePiece of magnetite
LoupeSmall, hand-held lens
LusterWay a mineral shines caused by reflected light
MaficRocks rich in magnesium and ferric compounds
MagmaHot, molten rock deep in the earth's crust that becomes lava in the surface
Magma ChamberUnderground reservoir of magma beneath a volcano
MantleLayer of the earth between the outer core and crust
Approximately 1,800 miles thick
MassiveHaving no definite crystal form or structure
MatrixMass of rock in which larger crystals or fossils are embedded
Metamorphic RockType of rock that has been changed by intense heat and/or pressure causing physical and chemical changes
MetamorphismProcess by which rocks and minerals are transformed by heat and pressure to create a new rock
MeteorRock from space that burns up as it enters the earth's atmosphere
MeteoritePiece of rock from space that hits the earth's surface without completely burning up
MicrocrystallineMineral structure in which the crystals are too small to be seen with the naked eye
MicrometeoriteMicroscopic meteorite
MicromountSmall mounted rock or mineral
MineralNaturally occurring, inorganic element or compound having an orderly internal structure and characteristic composition, crystal structure, and physical properties
Building blocks of rocks
Mineral VeinCracks in rocks that become filled with hot, mineral-rich liquids
MineralogistScientist who specializes in the study of minerals
MineralogyStudy of rock forming minerals
Mohs' ScaleScale devised by the Austrian mineralogist Friedrich Mohs that measures the relative hardness of minerals
Mold FossilFossilized imprint of the body of an organism (i.e., shell patterns)
Moqui MarbleDark brown concretion that weathers out of the Navajo Sandstone Formation in southern Utah
MoraineAccumulation of debris deposited by the outermost edge of a glacier
Mother LodePrincipal vein or lode
Richest and largest source of a desired mineral
MudstoneSedimentary rock composed of fine-grained particles
Muriatic AcidSee Hydrochloric Acid
NacreTiny platelets of calcium carbonate that create the soft sheen on pearls and inside some shells as they reflect light
Native ElementElement that occurs naturally uncombined with any other element
Nitric Acid(HNO3) Corrosive acid used in the manufacture of explosives and fertilizers
Very destructive liquid and will destroy many minerals
NoduleRounded lump of mineral found in sedimentary rock
Ocean SpreadingProcess in which oceans widen as new rock is brought up at the mid-ocean ridges
OolithSmall, rounded grains that make up some sedimentary rocks
OoliticMade mostly of ooliths
OpaqueDescribing a rock or mineral through which light does not pass
OrbicularContaining solidly encased orbs or sphercules with eye-like patterns
OreNatural material from which useful metals may be extracted
OutcropGeologist's term for the area in which rocks are exposed at the earth's surface
Oxalic Acid(HO2C-CO2H) Used for cleaning or bleaching, especially for the removal of rust
Oxidation ZoneUpper layer of mineral deposit where minerals are altered by oxygen and acids in water
PaleoecologyStudy of the ecology of fossil animals and plants
PaleontologyScience dealing with the life of past geological periods as known from fossil remains
PegmatiteVery coarse-grained igneous rock similar to granite in chemistry but characterized by very large mineral crystals
PeriodDivision of geological time lasting tens of millions of years
PermianGeological time period that stretched from about 300-250 million years ago
PetrifiedTurned to stone
Petrified FossilHighly porous organic material are replaced with minerals (i.e., petrified wood, Petoskey Stone)
PetrologistGeologist who specializes in the study of rocks
PetrologyBranch of geology that deals with the origin, occurrence, structure, and history of rocks
PhaneriticGrains visible with the naked eye
PhantomEarlier growth enclosed within a crystal
PhenocrystRelatively large crystal in igneous rock
Phosphoric Acid(H3PO4) Used in fertilizers, detergents, food flavoring, and pharmaceuticals or to remove rust from objects
Naval Jelly is a type of phosphoric acid
PiezoelectricityElectricity produced in a crystal by pressure
Pillow BasaltLava formed on the seabed consisting of pillow-shaped formations created when molten material contacted water
PlacerNatural deposit of valuable minerals, such as gold, washed into loose sediments such as river gravels
PlateLarge fragment of the earth's crust (AKA tectonic plate)
PlugSolidified core of an extinct volcano
PlutonLarge mass of igneous rock that formed beneath the earth's surface by solidification of magma
PolymorphsDifferent materials created by different crystals of the same chemical compound
PorphyriticIgneous rock containing lots of phenocrysts
Properties Characteristics of rocks or minerals by which they may be identified
Pry BarSteel tool used to move heavy rock or expand a crack
PsammologyBranch of geology relating to the study of sand
PseudofossilNatural object, structure, or mineral that resembles a fossil, but is not actually one
PseudomorphCrystal with the outward form of a different mineral species
PumiceBubbly lava that has solidified in a light, frothy state
PyroclastFragment of solid magma plug ejected during volcanic eruption
QuarrySteep-sided open excavation worked to remove rock
QuartzMost common mineral on the face of the earth
QuartziteConglomerate or sandstone that is comprised primarily of coarse quartz grains or pebbles converted to solid rock through metamorphic action
RecrystallizationFormation of new mineral grains in a rock while the rock is in a solid state
ReplacementSubstitution by mineral matter
Riker MountPaperbound, glass covered box for displaying specimens
RockMass of mineral material
Rock CycleContinuous cycle through which old rocks are transformed into new ones
RockhoundingAmateur geology
Rock SawSaws with circular disk blades with diamond rims
Round CutSee Brilliant Cut
RoughUncut or unpolished rock
SandstoneSedimentary rock mostly composed of sand-sized quartz grains
ScepterLarge crystal capping a slender crystal stem
Schiller EffectBrilliant play of bright colors in a crystal
ScreeMass of loose rubble and gravel on a mountain slope caused by weathering
Secondary Mineral Mineral that replaces another mineral as the result of weathering or alteration process
SedimentSolid grains that have settled out of water
Sedimentary RockType of rock that originates on the earth's surface and forms when sediment is compressed and cemented
SeismologyStudy of earthquakes
ShaftVertical mining excavation
SilicaSilicon dioxide
SillSheet-like igneous intrusion either near horizontal or following existing rock
Simple GreenEnvironmentally safe cleaner not harmful to many minerals
Slab SawSaw with blade ≥10" in diameter
SmeltingProcess by which a metal is removed from an ore
Sodium Bicarbonate(NaHCO3) Sodium bicarbonate reacts spontaneously with acids, releasing CO2 gas as a reaction product
Commonly used to neutralize unwanted acid solutions or acid spills
AKA baking soda
Specific GravityRatio of the mass of the mineral to the mass of an equal volume of water
SpeleogenesisFormation and development of caves
SpeleologyScientific study of caves
SpeleothemsSecondary mineral deposits formed in caves
StalactiteIcicle-shaped mineral deposit hanging from the roof of a cavern or cave
StalagmiteUpside down icicle-shaped mineral deposit that rises from the floor of a cavern or cave
StopeSeries of "step" above or below a mine level where ore has been extracted
StrataSequence of rock formations that can inform us of geological processes over time
StratificationBedding in sedimentary rock
StreakColor that a powdered mineral makes when rubbed across an unglazed tile
Strewn FieldGeographic area on the surface of the earth where meteorites from a single fall are dispersed
StriationMinute parallel groove or line on a crystal face
StromatoliteRocklike mound produced by microorganisms growing in shallow water
Subduction ZoneBoundary between two tectonic plates where one plate descends into the mantle beneath the other
Sulfuric Acid(H2SO4) Corrosive acid used for manufacturing chemicals, medicine, paints, detergents, and explosives
Very destructive liquid and will destroy many minerals
TalusSloping heap of naturally fallen debris at the base of a mountain or cliff
TectonicGeological processes within the earth that affect the earth's crust
Tectonic PlateOne of the approximately two-dozen giant slabs into which the earth's rigid surface is split
TektiteGlassy rock formed by a meteorite impact
ThundereggVolcanic nodule that typically features a rhyolitic outer shell and a central core of agate, opal, and/or crystals
Topographic MapMap of an area that depicts mountains and valleys by using "topographic contour lines"
TopographyGeneral shape of the surface of the earth
Trace FossilFossilized nests, burrows, gastroliths, footprints, etc. (i.e., dinosaur footprints)
TranslucentDescription of a material that light is able to pass through, but is not clear enough to look through
TransparentClear enough to look through
TrichroicShowing three different colors when viewed from different directions
TrilobitesGroup of prehistoric arthropods named after the three lengthways lobes of their bodies
Trim SawSaw with blade 4"-10" in diameter
True Form FossilFossil of actual plant or animal part (i.e., amber, mummies)
TV StoneSee Ulexite
Twin LawLaw stating the way in which the parts of a twin crystal are related
Twinned CrystalsTwo or more crystals of the same mineral that intersect each other along a common or shared plane
UlexiteBorate mineral composed of long, thin crystals that often occur as a blocky mass of fibrous veins
Ultramafic RockIgneous rock with a silica content of less than 45%
Ultraviolet LightType of light that is ling or short wave used to identify rocks that fluoresce
VeinThin, sheet-like fracture in a rock that is filled with secondary minerals
VertebratesAnimals with a backbone or spinal column
VesicleSmall cavity in extrusive rocks that is left by a gas bubble as the rock hardens
VinegarSee Acetic Acid
Vitreous LusterShine resembling that of glass
VolcanoVent or fissure in the earth's crust through which molten rock and hot gasses escape
Volcanic BombBlob of lava thrown out of a volcano
VugCavity in rock, often lined with crystals
WaxyTechnical term used to refer to the luster of a gemstone
WeatheringBreaking down of rocks and minerals by the action of various natural processes
XenolithCountry rock enclosed in magma
YellowcakeSolid form of mixed uranium oxide, which is produced from uranium ore in the uranium recovery process
ZeoliteMinerals that have a micro-porous structure
Sources: Gator Girl Rocks; Minerals.net; Wikipedia