Terminology
| Term | Definition |
|---|---|
| Abrasive | Substance used to cut and polish rocks Often called "grit" |
| Absolute hardness | Scale for measuring the hardness of a mineral |
| Absorption spectrum | Specific bands of light that pass through and those that get absorbed into a gem and disperse into the colors of the spectrum |
| Accessory mineral | Mineral that occurs with other minerals |
| Acetic Acid | (CH3COOH) Dissolves salts, sugars, and oils Vinegar is acetic acid mixed with water |
| Acicular | Aggregate of long, slender crystals |
| Acid | Group of chemicals containing a free hydrogen element |
| Acid Test | Procedure performed to help identify a mineral by using certain acids (usually hydrochloric and nitric) in contact with a mineral or its powder |
| Activator | Part in a fluorescent substance that causes the substance to glow when exposed to ultraviolet light |
| Adamantine | Describes the luster of transparent minerals that are very brilliant with a bright shine |
| Adit | Mine entryway Usually horizontal |
| Adularescence | Optical effect exhibited on certain minerals where they display a billowy, ghost-like reflection with a bluish-whitish color emanating from the surface |
| Agate | Type of microcrystalline (too small to see with the naked eye) quartz called chalcedony Usually forms in cavities in volcanic rocks |
| Agate Probe | Metal rod used to detect underground agates |
| Aggregate | Group of mineral crystals |
| Alkaline | Chemical substance that is either a hydroxide, carbonate, or metal oxide that has the ability to react with acids to form salts |
| Alloy | Mixture of two or more metals or semi-metals in which the atoms of the different metals are intermingled among each other |
| Alluvial | Eroded material that gets transported by rivers or streams |
| Alluvial deposit | Deposit in a stream or river where alluvial materials collect |
| Alpine | Environment in a mountainous region, often referring to granite zones within the Alps of Europe |
| Alpine Cavity | Specific type of cavity within rock in mountainous regions that is created from the geological stretching and bending of rock |
| Amalgam | Alloy of mercury and another metal |
| Amber | Gem made from hardened resin of ancient trees |
| Amethyst | Pale purple to violet (due to iron compounds) variety of crystalline quartz |
| Amorphous | Non-crystalline |
| Amphibole group | Group of minerals that contain iron, magnesium, silicon, oxygen, and hydroxyl Very similar to pyroxenes, but occur in longer, thinner crystals |
| Amygdaloidal Rock | Volcanic rock containing numerous gas cavities filled with secondary material (ie., quartz, calcite, chalcedony, zeolite) |
| Amygdule | Mineral-filled cavity or vesicle in a volcanic rock |
| Anhydrous | Minerals that contain no water in their chemical structure |
| Anisotropic | Lacking consistent hardness on all surfaces |
| Anticline | Fold in rock where the strata protrudes upwards towards the fold |
| Antimonides | Group of sulfides that contain one or more true metals combined with antimony |
| Apatite group | Minerals that are isomorphous hexagonal phosphates |
| Aqueous | Formed from precipitating hard water |
| Arête | Narrow mountain ridge formed between two glacial valleys or cirques |
| Argonite Group | Group of minerals belonging to the carbonate group that are isomorphous with one another Well-known members include Aragonite, Cerussite, and Strontianite |
| Argentiferous | Containing silver |
| Argillacious | Composed mostly of clay |
| Arid | Dry, desert region |
| Arsenates | Group 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 |
| Arsenides | Group of sulfides that contain one or more true metals with arsenic |
| Asbestos | Any of the several fibrous minerals belonging to both the Serpentine group and the Amphibole group |
| Asterism | Property of reflecting light in star-like patterns of 4, 6, or 12 rays |
| Asymetrical | Not containing perfect symmetry |
| Atomic Structure | Arrangement and the type of atoms that exist in a particular structure |
| Auriferous | Containing gold |
| Autochthonous | Rock or mineral that formed in the same location where it was found |
| Aventurescence | Effect 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 |
| Banding | Presence of color zoning lines, or "bands" in some minerals |
| Basal | Type of cleavage exhibited on a horizontal plane of a mineral by way of its base |
| Basalt | Igneous rock |
| Batholith | Very large mass of igneous rock |
| Bauxite | Rock ore from which aluminum is refined |
| Bead Test | Complex, 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 |
| Bedding | Layering of sedimentary rocks |
| Bedrock | Layer of solid rock underneath loose material such as soil or sand |
| Belemnite | Fossil of an extinct marine creature similar to squid but possessing a hard internal skeleton and lacking tentacles |
| Biogenic Rock | Rock formed by organic action |
| Bypyramid | Crystal shape in form with a plane dividing a crystal into two pyramids base to base |
| Birefringence | Optical effect commonly known as double refraction |
| Bitumen | Organic, naturally occurring form of petroleum with a tar-like consistency |
| Bladed | Crystal habit describing flat, elongated, "knife-like" crystals |
| BLM | Bureau of Land Management |
| Bond | Link between atoms to form a secure molecule |
| Borates | Group of minerals that are compounds of one or more metallic elements combined with the borate radical |
| Botryoidal | Formed into masses of small spherical bulges |
| Breccia | Sedimentary rock made of jagged or angular mineral fragments cemented together |
| Brilliant Cut | Type of rounded cut used for gemstones to maximize brilliance and fire AKA round cut |
| Brittle | Form of tenacity which describes a mineral that gets hammered or scratched and results in a fine powder or small crumbs |
| Bronze | Collective term describing any metallic alloy that ranges in color from light yellow to orange |
| Bullion | Precious metal cast in bulk form such as bars, bricks, or ingots |
| Cabochon | Rock cut so that its top has a smooth domed surface with no facets |
| Calcareous | Composed of calcite or calcium carbonate |
| Calcite | Main mineral in limestone and chalk Chemical name = calcium carbonate |
| Cameo | Gem with a design or figure carved out of stone and raised above the background layer |
| Canyon | Deep, narrow valley often formed when a river cuts through rock |
| Capillary | Aggregate composed of tiny, long, and slender (hair like) crystal strands |
| Carat | Standard measure of weight for precious gems and minerals 1ct = 0.006oz = 0.2g |
| Carbonates | Mineral group whose members contain one or more metallic elements plus the carbonate radical |
| Carbonatite | Type of igneous rock mostly of carbonate minerals |
| Carbon Fossil | Delicate 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) |
| Carboniferous | Geological time period that stretches from around 365 - 290 million years ago |
| Cast | Fossil formed by the filling of a mold |
| Cast Fossil | Mineral 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 effect | See chatoyancy |
| Cave | Naturally formed opening in the ground that extends beyond the zone of light and is large enough for a person to enter |
| Cavity | Hollow area in rock that develops because of some form of stress |
| Cementation Zone | Underground area where certain elements are concentrated and can combine to form primary minerals |
| Chemical Sedimentary Rock | Rock that is formed by mineral precipitation |
| Chert | Fine-grained, usually dark-colored sedimentary rock of silica-rich composition |
| Chitin | Horny substance that forms the shells of arthropods |
| Chondrite | Type of stony meteorite formed mostly on chondrules Generally composed from pyroxenes and Olivine and contain Iron-nickel |
| Chondrules | Small, millimeter sized spherical grains that were once molten and came together in space through gravitational accretion |
| Chromates | Group of minerals that are compounds of one or more metallic elements combined with the chromate radical Usually brightly colored and heavy |
| Cinder Cone | Naturally expelled debris, usually in a conical pile, surrounding the vent of a volcano |
| Cirque | Steep-sided, bowl-shaped hollow in a mountain, carved out by a glacier |
| Claim | Tract of public land staked out to mine |
| Clast | Fragment of broken rock |
| Clastic Sediment | Sedimentary rock made mainly of broken rock fragments |
| Clay | Mineral particles that are smaller than 0.00008" (0.002mm) wide and are common in soil and sediment |
| Cleavage | The way certain minerals break along planes according to the mineral's atomic structure |
| Clinopinacoid | Elongated crystal with steep, slanty angle towards its top at the base |
| Cluster | Dense agglomeration of crystals |
| Coal | Dark gray to black, staining and greasy rock formed by the accumulation and compaction of herbal organic materials |
| Coating | Thin layer of one material on the surface of another |
| Columnar | Like columns |
| Compostion | Elements and quantity of elements a substance contains |
| Compound | Two or more elements joined together chemically |
| Compression Fossil | Fossil preserved in sedimentary rock that has undergone physical compression |
| Concentrates | Material that has been processed and reduced by removing large rocks and organic material |
| Concentric | Form of banding where the bands are circular, forming rounded or oval-shaped rings around a central point |
| Conchoidal | Concave fracture in a glassy mineral |
| Concretion | Distinct, hard, compact mass or aggregate of mineral matter that is normally rounded |
| Conductivity | Ability of a substance to act as a conductor of electricity |
| Conductor | Substance capable of transmitting electricity Substance that is able to retain heat or pressure |
| Conflict Minerals | Minerals that are mined in war zones to finance terrorist or revolutionary groups |
| Conglomerate | Sedimentary rock made up of pieces of rocks that have been worn into rounded shapes and naturally cemented together |
| Conodonts | Teeth of very early fish-like creatures that lived about 515 million - 210 million years ago |
| Contact Metamorphic Rock | Rock that forms as the heat from magma or a lava flow alters an existing rock |
| Coprolite | Fossilized dung |
| Coral | Skeletons of tiny sea animals that live in colonies combined with calcium carbonate into a hard limestone |
| Core | Center of the earth, made of heavy metals ~850 miles wide |
| Country Rock | Rock that surrounds a mineral deposit or igneous intrusion |
| Coxcomb | Aggregate composed of flaky or tabular crystals that are joined from a base with grooves between long, slender, arc-like crystals |
| Crater | Natural depression marking the vent of a volcano or impact site of a meteorite |
| Craton | Ancient part of a continent unaltered for at least 1 billion years |
| Crazing | Condition in Opal or some other gemstones such as Amber that cause them to form internal or surface cracks |
| Cretaceous | Geological time period that stretched from about 145-65 millions years ago |
| Crinoids | Large class of echinoderms usually have a cup-shaped body with 5 or more feathery arms |
| Crust | Thin outer layer of the earth that lies over the mantle 4-45 miles thick |
| Cryptocrystalline | Rock surface of solid rock that is comprised of extremely minute or microscopic crystals |
| Crystal | Geometric shape which many minerals form |
| Crystal Form | Way in which different faces of crystals are arranged |
| Crystal Habit | Typical shape in which a crystal or cluster of crystals grow |
| Crystal System | Different groups into which crystals may be placed according to symmetry |
| Crystallography | Science and study of the formations and mathematics of crystals |
| Cubic | Shaped as a cube |
| Culet | Bottom point of a faceted gem |
| Cut | Description of the type of facet of a gem |
| Cyclosilicates | Group of silicates that have their tetrahedrons linked into rings |
| Cymophane Effect | Phenomenon 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 Number | Number assigned to each mineral according to classification system devised by James Dwight Dana |
| Dendrites | Fern-like growths of crystals lining the cracks and joints in rocks |
| Deposit | Lay down material such as mud, sand, or gravel in a new location |
| Desert | Arid region that typically receives less than 10" on rain each year |
| Desert Rose | Nickname for rosette-shaped gypsum concretions and barite formations |
| Devonian | Geological time period that stretches from about 415-360 million years ago |
| Diatom | Fossilized microscopic marine plant |
| Dichroic | Showing different colors when viewed from different directions |
| Dike/Dyke | Sheet-like igneous intrusion that is near vertical or cuts across existing rock |
| Dinosaurs | Group of extinct prehistoric reptiles that lived 230-65 million years ago |
| Dip | Downward angle of inclination of bedrock from the horizontal |
| Doublet | Composite stone made of 2 pieces cemented or glued together |
| Dredge | Mining 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) |
| Druzy | Crust of uniformly tiny crystals filling a cavity or coating a rock |
| Dumpsite | At a mine site, where the non-economic rocks are deposited |
| Electrum | Natural mix of gold and silver |
| Element | Material that cannot be broken down into more simple substances by chemical means |
| Enhydro | Crystal that contains a fluid-filled cavity |
| Eocene | Epoch of the Tertiary Period between the Paleocene and Oligocene, about 55-35 million years ago |
| Epoch | Division of geological time, part of a period |
| Era | Largest division of geological time lasting hundreds of millions of years |
| Erosion | Wearing away and removal of exposed material by water, wind, and ice |
| Erratic | Large rock that has been carried by a glacier and dropped from it place of origin |
| Erosion | Wearing away of the material on the Earth's surface |
| Eruption | Discharge of lave, pyroclastic material, or gas from a volcanic cone or vent |
| Evaporite | Natural salt or mineral formed by the process of evaporation |
| Exfoliation | Process of weathered rock sheets splitting away in layers from larger rock masses |
| Exposure | Where a rock outcrop is exposed at the surface |
| Extrusive Igneous Rock | Igneous rock that forms at the earth's surface |
| Facet | Flat surface on a cut gemstone |
| Fault | Long fracture in rock along which rock masses move |
| Feldspar | Most common, rock-forming minerals, constituting 60% of the earth's crust |
| Feldspathic | Rock containing feldspar |
| Felsic | Rock rich in feldspar and silica |
| Fire Agate | Form of chalcedony that contains inclusion of iron oxides that result in a play of colors like an opal |
| Fissure Volcano | Volcano that erupts through a long crack |
| Float | Pieces of rock that have moved from their original source |
| Flood Basalt | Plateau formed from huge eruption of basalt from fissure |
| Flowstone | General term for the sheet-like mineral deposit on a cave wall or floor |
| Fluorescence | Emission of brightly colored light by a substance when exposed to ultraviolet light rays |
| Foliation | Flat layers of minerals in metamorphic rock formed as minerals recrystallize under pressure |
| Fool’s Gold | Pyrite |
| Formation | Related deposit of rocks formed during the same time period and generally under the same circumstances |
| Fortification | Form of agate with angled concentric banding |
| Fossil | Remains, traces, or impressions of organisms that lived millions of years ago and are usually preserved in rocks |
| Fossil Fuels | Coal, oil, and natural gas which are formed from the remains of once-living organisms |
| Fracture | Way in which a rock or mineral breaks when it doesn't break along cleavage planes |
| Fulgurite | Sand fused by lightning |
| Fumarole | Hole or vent through which volcanic gases escape |
| Gangue | Waste rock in a mineral deposit that is being worked |
| Gastroliths | Stones, swallowed by dinosaurs or other animals, used to help grind up food |
| Gemstone | Mineral, usually crystalline, that derives particular value from its beauty, color, rarity, and hardness |
| Geode | Rock containing a crystal-lined cavity in which crystals grow toward the center |
| Geologic Time Chart | Record of divisions of the Earth's history |
| Geological Column | Diagram depicting the successive layers of strata that have formed over geologic time |
| Geologist | Someone who studies the earth |
| Glacier | Large mass of ice that forms on land and flows slowly downhill under its own weight |
| Gold Dore | Bar of gold that is usually about 90% pure |
| Grain | Particle of a mineral |
| Graphite | Mineral made entirely of carbon |
| Grubstake | Supplies furnished to a prospector in return for a share in discoveries |
| Habit | General shape or appearance of a mineral |
| Hackly Fracture | Jagged breakage of a metal |
| Hardness | Degree of resistance of a rock or mineral to being scratched |
| Horn | Steep-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 |
| Hydrothermal | Water heated by magma |
| Hydrothermal Deposit | Mineral deposit formed from mineral-rich hydrothermal fluids |
| Ice Age | Usually referring to the most recent ice age, a portion of the Pleistocene epoch from 1.8 million - 11,000 years ago |
| Ichnofossils | Sedimentary structures consisting of a fossilized track, trail, burrow, or tube resulting from the life activities and behavior of an animal |
| Ichnologist | Scientist who studies fossilized footprints, tracks, and other trace fossils |
| Igneous Rock | Type of rock that forms as lava or magma cools and hardens |
| Impact Crater | Crater formed by the impact of a meteorite |
| Inclusion | Presence of foreign body within a crystal |
| Index Fossil | Key fossil used to correlate strata |
| Intrusion | Emplacement of magma into existing rock |
| Intrusive Igneous Rock | Igneous rock that forms beneath the surface of the earth |
| Invertebrates | Animals lacking a backbone or spinal column |
| Iridescence | Play of colors on the surface of a mineral |
| Island Arc | Curved chain of volcanic islands in a subduction zone |
| Jet | Form of coal that can be polished to look like black glass |
| Jurassic | Geological time period that stretched from 200-145 million years ago |
| K-T Extinction / Boundary Event | Approximately 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 |
| Karat | Parts per 24 of pure gold in an alloy |
| Karst Topography | Geologic 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 |
| Kimberlite | Igneous rocks rich in volatiles, normally forming pipes |
| Knapping | Process of chipping away at a stone to produce projective points, knives, and other objects |
| Laccolith | Mass of intrusive igneous rock with a dome-shaped top and flat base |
| Lapidary | Craftsperson who cuts and polishes gemstones |
| Last Chance Gulch | Location of significant gold rush in Helena, Montana |
| Lava | Hot melted rock that flows out of an erupting volcano |
| Lava Tube | Hollow 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 |
| Leaverite | Rockhounder slang for a rock that isn't worth carrying back home |
| Lithophysae | Scientific name for a thunderegg |
| Lithosphere | Portion of the earth comprising the crust and upper-most portion of the solid mantle |
| Locate | Mark the boundaries of a claim |
| Lodestone | Piece of magnetite |
| Loupe | Small, hand-held lens |
| Luster | Way a mineral shines caused by reflected light |
| Mafic | Rocks rich in magnesium and ferric compounds |
| Magma | Hot, molten rock deep in the earth's crust that becomes lava in the surface |
| Magma Chamber | Underground reservoir of magma beneath a volcano |
| Mantle | Layer of the earth between the outer core and crust Approximately 1,800 miles thick |
| Massive | Having no definite crystal form or structure |
| Matrix | Mass of rock in which larger crystals or fossils are embedded |
| Metamorphic Rock | Type of rock that has been changed by intense heat and/or pressure causing physical and chemical changes |
| Metamorphism | Process by which rocks and minerals are transformed by heat and pressure to create a new rock |
| Meteor | Rock from space that burns up as it enters the earth's atmosphere |
| Meteorite | Piece of rock from space that hits the earth's surface without completely burning up |
| Microcrystalline | Mineral structure in which the crystals are too small to be seen with the naked eye |
| Micrometeorite | Microscopic meteorite |
| Micromount | Small mounted rock or mineral |
| Mineral | Naturally occurring, inorganic element or compound having an orderly internal structure and characteristic composition, crystal structure, and physical properties Building blocks of rocks |
| Mineral Vein | Cracks in rocks that become filled with hot, mineral-rich liquids |
| Mineralogist | Scientist who specializes in the study of minerals |
| Mineralogy | Study of rock forming minerals |
| Mohs' Scale | Scale devised by the Austrian mineralogist Friedrich Mohs that measures the relative hardness of minerals |
| Mold Fossil | Fossilized imprint of the body of an organism (i.e., shell patterns) |
| Moqui Marble | Dark brown concretion that weathers out of the Navajo Sandstone Formation in southern Utah |
| Moraine | Accumulation of debris deposited by the outermost edge of a glacier |
| Mother Lode | Principal vein or lode Richest and largest source of a desired mineral |
| Mudstone | Sedimentary rock composed of fine-grained particles |
| Muriatic Acid | See Hydrochloric Acid |
| Nacre | Tiny platelets of calcium carbonate that create the soft sheen on pearls and inside some shells as they reflect light |
| Native Element | Element 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 |
| Nodule | Rounded lump of mineral found in sedimentary rock |
| Ocean Spreading | Process in which oceans widen as new rock is brought up at the mid-ocean ridges |
| Oolith | Small, rounded grains that make up some sedimentary rocks |
| Oolitic | Made mostly of ooliths |
| Opaque | Describing a rock or mineral through which light does not pass |
| Orbicular | Containing solidly encased orbs or sphercules with eye-like patterns |
| Ore | Natural material from which useful metals may be extracted |
| Outcrop | Geologist'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 Zone | Upper layer of mineral deposit where minerals are altered by oxygen and acids in water |
| Paleoecology | Study of the ecology of fossil animals and plants |
| Paleontology | Science dealing with the life of past geological periods as known from fossil remains |
| Pegmatite | Very coarse-grained igneous rock similar to granite in chemistry but characterized by very large mineral crystals |
| Period | Division of geological time lasting tens of millions of years |
| Permian | Geological time period that stretched from about 300-250 million years ago |
| Petrified | Turned to stone |
| Petrified Fossil | Highly porous organic material are replaced with minerals (i.e., petrified wood, Petoskey Stone) |
| Petrologist | Geologist who specializes in the study of rocks |
| Petrology | Branch of geology that deals with the origin, occurrence, structure, and history of rocks |
| Phaneritic | Grains visible with the naked eye |
| Phantom | Earlier growth enclosed within a crystal |
| Phenocryst | Relatively 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 |
| Piezoelectricity | Electricity produced in a crystal by pressure |
| Pillow Basalt | Lava formed on the seabed consisting of pillow-shaped formations created when molten material contacted water |
| Placer | Natural deposit of valuable minerals, such as gold, washed into loose sediments such as river gravels |
| Plate | Large fragment of the earth's crust (AKA tectonic plate) |
| Plug | Solidified core of an extinct volcano |
| Pluton | Large mass of igneous rock that formed beneath the earth's surface by solidification of magma |
| Polymorphs | Different materials created by different crystals of the same chemical compound |
| Porphyritic | Igneous rock containing lots of phenocrysts |
| Properties | Characteristics of rocks or minerals by which they may be identified |
| Pry Bar | Steel tool used to move heavy rock or expand a crack |
| Psammology | Branch of geology relating to the study of sand |
| Pseudofossil | Natural object, structure, or mineral that resembles a fossil, but is not actually one |
| Pseudomorph | Crystal with the outward form of a different mineral species |
| Pumice | Bubbly lava that has solidified in a light, frothy state |
| Pyroclast | Fragment of solid magma plug ejected during volcanic eruption |
| Quarry | Steep-sided open excavation worked to remove rock |
| Quartz | Most common mineral on the face of the earth |
| Quartzite | Conglomerate or sandstone that is comprised primarily of coarse quartz grains or pebbles converted to solid rock through metamorphic action |
| Recrystallization | Formation of new mineral grains in a rock while the rock is in a solid state |
| Replacement | Substitution by mineral matter |
| Riker Mount | Paperbound, glass covered box for displaying specimens |
| Rock | Mass of mineral material |
| Rock Cycle | Continuous cycle through which old rocks are transformed into new ones |
| Rockhounding | Amateur geology |
| Rock Saw | Saws with circular disk blades with diamond rims |
| Round Cut | See Brilliant Cut |
| Rough | Uncut or unpolished rock |
| Sandstone | Sedimentary rock mostly composed of sand-sized quartz grains |
| Scepter | Large crystal capping a slender crystal stem |
| Schiller Effect | Brilliant play of bright colors in a crystal |
| Scree | Mass 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 |
| Sediment | Solid grains that have settled out of water |
| Sedimentary Rock | Type of rock that originates on the earth's surface and forms when sediment is compressed and cemented |
| Seismology | Study of earthquakes |
| Shaft | Vertical mining excavation |
| Silica | Silicon dioxide |
| Sill | Sheet-like igneous intrusion either near horizontal or following existing rock |
| Simple Green | Environmentally safe cleaner not harmful to many minerals |
| Slab Saw | Saw with blade ≥10" in diameter |
| Smelting | Process 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 Gravity | Ratio of the mass of the mineral to the mass of an equal volume of water |
| Speleogenesis | Formation and development of caves |
| Speleology | Scientific study of caves |
| Speleothems | Secondary mineral deposits formed in caves |
| Stalactite | Icicle-shaped mineral deposit hanging from the roof of a cavern or cave |
| Stalagmite | Upside down icicle-shaped mineral deposit that rises from the floor of a cavern or cave |
| Stope | Series of "step" above or below a mine level where ore has been extracted |
| Strata | Sequence of rock formations that can inform us of geological processes over time |
| Stratification | Bedding in sedimentary rock |
| Streak | Color that a powdered mineral makes when rubbed across an unglazed tile |
| Strewn Field | Geographic area on the surface of the earth where meteorites from a single fall are dispersed |
| Striation | Minute parallel groove or line on a crystal face |
| Stromatolite | Rocklike mound produced by microorganisms growing in shallow water |
| Subduction Zone | Boundary 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 |
| Talus | Sloping heap of naturally fallen debris at the base of a mountain or cliff |
| Tectonic | Geological processes within the earth that affect the earth's crust |
| Tectonic Plate | One of the approximately two-dozen giant slabs into which the earth's rigid surface is split |
| Tektite | Glassy rock formed by a meteorite impact |
| Thunderegg | Volcanic nodule that typically features a rhyolitic outer shell and a central core of agate, opal, and/or crystals |
| Topographic Map | Map of an area that depicts mountains and valleys by using "topographic contour lines" |
| Topography | General shape of the surface of the earth |
| Trace Fossil | Fossilized nests, burrows, gastroliths, footprints, etc. (i.e., dinosaur footprints) |
| Translucent | Description of a material that light is able to pass through, but is not clear enough to look through |
| Transparent | Clear enough to look through |
| Trichroic | Showing three different colors when viewed from different directions |
| Trilobites | Group of prehistoric arthropods named after the three lengthways lobes of their bodies |
| Trim Saw | Saw with blade 4"-10" in diameter |
| True Form Fossil | Fossil of actual plant or animal part (i.e., amber, mummies) |
| TV Stone | See Ulexite |
| Twin Law | Law stating the way in which the parts of a twin crystal are related |
| Twinned Crystals | Two or more crystals of the same mineral that intersect each other along a common or shared plane |
| Ulexite | Borate mineral composed of long, thin crystals that often occur as a blocky mass of fibrous veins |
| Ultramafic Rock | Igneous rock with a silica content of less than 45% |
| Ultraviolet Light | Type of light that is ling or short wave used to identify rocks that fluoresce |
| Vein | Thin, sheet-like fracture in a rock that is filled with secondary minerals |
| Vertebrates | Animals with a backbone or spinal column |
| Vesicle | Small cavity in extrusive rocks that is left by a gas bubble as the rock hardens |
| Vinegar | See Acetic Acid |
| Vitreous Luster | Shine resembling that of glass |
| Volcano | Vent or fissure in the earth's crust through which molten rock and hot gasses escape |
| Volcanic Bomb | Blob of lava thrown out of a volcano |
| Vug | Cavity in rock, often lined with crystals |
| Waxy | Technical term used to refer to the luster of a gemstone |
| Weathering | Breaking down of rocks and minerals by the action of various natural processes |
| Xenolith | Country rock enclosed in magma |
| Yellowcake | Solid form of mixed uranium oxide, which is produced from uranium ore in the uranium recovery process |
| Zeolite | Minerals that have a micro-porous structure |
