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  2. Quartz - Wikipedia

    en.wikipedia.org/wiki/Quartz

    Quartz is, therefore, classified structurally as a framework silicate mineral and compositionally as an oxide mineral. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar. [10] Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral. The transformation ...

  3. Tourmaline - Wikipedia

    en.wikipedia.org/wiki/Tourmaline

    Tri-chromatic elbaite crystals on quartz, Himalaya Mine, San Diego Co., California, US Tourmaline is a six-member ring cyclosilicate having a trigonal crystal system. It occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section, often with curved striated faces.

  4. Pegmatite - Wikipedia

    en.wikipedia.org/wiki/Pegmatite

    Quartz crystals with masses measured in thousands of pounds [5] and micas over 10 meters (33 ft) across and 4 meters (13 ft) thick have been found. [8] Spodumene crystals over 12 meters (40 ft) long have been found in the Black Hills of South Dakota , and beryl crystals 8.2 meters (27 ft) long and 1.8 meters (6 ft) in diameter have been found ...

  5. List of mineral symbols - Wikipedia

    en.wikipedia.org/wiki/List_of_mineral_symbols

    Mineral symbols (text abbreviations) are used to abbreviate mineral groups, subgroups, and species, just as lettered symbols are used for the chemical elements.. The first set of commonly used mineral symbols was published in 1983 and covered the common rock-forming minerals using 192 two- or three-lettered symbols. [1]

  6. Flint - Wikipedia

    en.wikipedia.org/wiki/Flint

    Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, [1] [2] categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires .

  7. Smoky quartz - Wikipedia

    en.wikipedia.org/wiki/Smoky_quartz

    Smoky quartz is a brownish grey, translucent variety of quartz that ranges in clarity from almost complete transparency to an almost-opaque brownish-gray or black crystals. [6] The color of smoky quartz is produced when natural radiation, emitted from the surrounding rock, activates color centers around aluminum impurities within the ...

  8. Ball clay - Wikipedia

    en.wikipedia.org/wiki/Ball_clay

    The ceramic use of ball clays in Britain dates back to at least the Roman era. More recent trade began when a clay was needed to make tobacco pipes in the 16th and 17th century. [ 8 ] In 1771 Josiah Wedgwood signed a contract for 1,400 tons a year of ball clay with Thomas Hyde of Purbeck , enabling the production of thinner-walled ceramics.

  9. Porphyry (geology) - Wikipedia

    en.wikipedia.org/wiki/Porphyry_(geology)

    "Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.

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