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2. Crystal cluster - Wikipedia

   en.wikipedia.org/wiki/Crystal_cluster

   A crystal cluster is a group of crystals which are formed in an open space environment and exhibit euhedral crystal form determined by their internal crystal structure. [ 1 ] [ 2 ] A cluster of small crystals coating the walls of a cavity are called druse .

3. Herkimer diamond - Wikipedia

   en.wikipedia.org/wiki/Herkimer_diamond

   Herkimer diamonds are double-terminated quartz crystals discovered within exposed outcrops of dolomite in and around Herkimer County, New York, and the Mohawk River Valley in the US. [ 1 ] [ 2 ] They are not diamonds ; the "diamond" in their name is due to both their clarity and well formed faces.

4. Quartz - Wikipedia

   en.wikipedia.org/wiki/Quartz

   A synthetic quartz crystal grown by the hydrothermal method, about 19 centimetres (7.5 in) long and weighing about 127 grams (4.5 oz) Not all varieties of quartz are naturally occurring. Some clear quartz crystals can be treated using heat or gamma-irradiation to induce color where it would not otherwise have occurred naturally. Susceptibility ...

5. Amethyst - Wikipedia

   en.wikipedia.org/wiki/Amethyst

   Artigas, Uruguay and neighboring Brazilian state Rio Grande do Sul are large world producers, with lesser quantities mined in Minas Gerais and Bahia states. [14] An amethyst geode that formed when large crystals grew in open spaces inside the rock. The largest amethyst geode found as of 2007 was the Empress of Uruguay, found in Artigas, Uruguay ...

6. 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 ...

7. Dynamic quartz recrystallization - Wikipedia

   en.wikipedia.org/wiki/Dynamic_quartz_re...

   The at-large proportion and structure of the original quartz crystals is preserved to the greatest extent, compared with the other profiles. Formed by a combination of the two mechanisms mentioned, limited crystal plasticity (due to low temperature) prevents any further separation of subgrains.