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flint, mineral
(Encyclopedia)flint, variety of quartz that commonly occurs in rounded nodules and whose crystal structure is not visible to the naked eye. Flint is dark gray, smoky brown, or black in color; pale gray flint is cal...abrasive
(Encyclopedia)abrasive, material used to grind, smooth, cut, or polish another substance. Natural abrasives include sand, pumice, corundum, and ground quartz. Carborundum (silicon carbide) and alumina (aluminum oxi...topaz
(Encyclopedia)topaz tōˈpăz [key], aluminum silicate mineral with either hydroxyl radicals or fluorine, Al2SiO4(F,OH)2, used as a gem. It is commonly colorless or some shade of pale yellow to wine-yellow; pale bl...agate
(Encyclopedia)agate ăgˈĭt [key], translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-e...sandpaper
(Encyclopedia)sandpaper, abrasive originally made by gluing grains of sand to heavy paper sheets. Today sandpaper is made primarily with quartz, aluminum oxide, or silicon carbide grains, and is graded according to...schist
(Encyclopedia)schist shĭst [key], metamorphic rock having a foliated, or plated, structure called schistosity in which the component flaky minerals are visible to the naked eye. Schists are distinguished from the ...geode
(Encyclopedia)geode jēˈōd [key], hollow, globular rock nodule ranging in diameter from 1 to 12 in. (2.54–30.5 cm) or more. Most geodes are partly filled with mineral matter; they have a thin layer of chalcedon...Goiás
(Encyclopedia)Goiás goi-äsˈ [key], state, 211,941 sq mi (548,927 sq km), central Brazil. Goiânia is the capital. The ...Atlin Lake
(Encyclopedia)Atlin Lake ătˈlĭn [key], long, irregular mountain lake, c.300 sq mi (780 sq km), NW British Columbia, Canada, touching the Yukon boundary. It is the source of the Yukon River. The town of Atlin is ...scheelite
(Encyclopedia)scheelite shāˈlīt, shēˈ– [key], heavy white or yellow mineral, calcium tungstate, CaWO4, crystallizing in the tetragonal system. It is found in granite pegmatites, in contact-metamorphic deposi...Browse by Subject
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