Colored Stones 2 Key Terms PDF

Colored Stones 2 Key Terms Alluvial deposit—A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated. Orogenic belt—A long, widespread area in the earth’s crust where tectonic events cause major structural changes, often forming mountain...

Colored Stones 2 Key Terms Alluvial deposit—A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated. Orogenic belt—A long, widespread area in the earth’s crust where tectonic events cause major structural changes, often forming mountain ranges. Artisanal miner—An independent gem or mineral prospector who typically uses small-scale, nonmechanized recovery methods. Overburden—The material covering a gem deposit that must be removed before production can begin. Contact metamorphism—Localized changes caused by an igneous intrusion that takes place where the magma meets the surrounding rock. Core—The earth’s innermost layer. Crust—The surface and outermost layer of the earth. Eluvial deposit—A deposit where gems are eroded from the source rock but remain in place close to the source. Pegmatite—An igneous rock typically formed from cooling, once-molten granite that follows fractures in its surrounding rock. Placer—Workable alluvial deposit of gem minerals with economic potential. Plate—A section of the earth’s rigid outer crust. Plate tectonics—Study of the formation, structure, and movement of the plates of the earth’s crust. Erosion—The wearing away and transport of rock materials by natural forces. Pneumatolysis—Crystallization of minerals from a gas. Geode—A spherical, often hollow, mineral-lined cavity in rock. Primary deposit—Gems found in the rocks that they formed in. Heavy minerals—Minerals dense enough to become concentrated and separated from lighter ones by the action of surface water. Regional metamorphism—Changes in rock type and minerals over a wide area, caused by heat and pressure of large-scale geological events. Hydrothermal fluid—Hot, high-pressure solution that can dissolve, transport, and deposit minerals from one place to another. Rock cycle—A constant formation and recycling process that creates new rock from old. Igneous rock—Rock formed by the crystallization of molten material. Secondary deposit—Gems found away from their primary source. Intrusion—Large mass of igneous rock that crystallizes underground without reaching the surface. Sedimentary rock—Rock produced from the eroded and weathered remains of existing rocks. Magma—General term for any molten rock. Mantle—A layer between the earth’s crust and its core. Subduction—A process that occurs when two of the earth’s plates collide, forcing one under the other. Mantle convection—Circulation in the mantle that drives the movement of the earth’s plates. Vein—A mineral deposit that occupies an existing fissure or fracture in the rock. Metamorphic rock—A category of rocks that have been altered by heat and pressure. Volcanic—Pertaining to igneous activity at the earth’s surface, where magma erupts through a volcano or fissure. Metasomatism—A type of metamorphism where chemical changes in the minerals and rocks result from the introduction of material from external sources, often as hydrothermal solutions. 86 Xenocryst—A “foreign crystal” that forms in unrelated rocks and is brought to the surface as a passenger in magma.