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2. Quartz - Wikipedia

   en.wikipedia.org/wiki/Quartz

   Citrine is a variety of quartz whose color ranges from pale yellow to brown due to a submicroscopic distribution of colloidal ferric hydroxide impurities. [40] Natural citrines are rare; most commercial citrines are heat-treated amethysts or smoky quartzes. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a ...

3. Chalcedony - Wikipedia

   en.wikipedia.org/wiki/Chalcedony

   Chalcedony. Chalcedony (/ kælˈsɛdəni / kal-SED-ə-nee, or / ˈkælsəˌdoʊni / KAL-sə-doh-nee) [2] is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. [3] These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic.

4. Quartzite - Wikipedia

   en.wikipedia.org/wiki/Quartzite

   Quartzite is a very hard rock composed predominantly of an interlocking mosaic of quartz crystals. The grainy, sandpaper-like surface is glassy in appearance. Minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization, causing streaks and lenses to form within the quartzite. [1 ...

5. Amethyst - Wikipedia

   en.wikipedia.org/wiki/Amethyst

   Amethyst is a purple variety of quartz (SiO. 2) and owes its violet color to irradiation, impurities of iron (Fe3+. ) and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. [2][3][4] The irradiation causes the iron Fe3+.

6. Chert - Wikipedia

   en.wikipedia.org/wiki/Chert

   Chalcedony is a microfibrous quartz. [16] Agate is distinctly banded chalcedony with successive layers differing in color or value. [66] Onyx is a banded agate with layers in parallel lines, often black and white (sardonyx). [67] Magadi-type chert is a variety that forms from a sodium silicate precursor in highly alkaline lakes such as Lake ...

7. Smoky quartz - Wikipedia

   en.wikipedia.org/wiki/Smoky_quartz

   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 ...