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2. 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. Because the first discovery sites were in the village ...

3. Bristol Diamonds - Wikipedia

   en.wikipedia.org/wiki/Bristol_Diamonds

   Bristol Diamonds are quartz crystals found in geodes and geological rock formations which occur in dolomitic conglomerate in the Avon Gorge in Bristol, England. Their origin lies in geological processes of the Triassic period, about 250 to 200 million years ago. The Bristol Diamonds became popular novelties for visitors to the spa at Hotwells ...

4. Quartz - Wikipedia

   en.wikipedia.org/wiki/Quartz

   Quartz. Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO 4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2. Quartz is, therefore, classified structurally as a framework silicate mineral ...

5. 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 ...

6. 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+.

7. Cristobalite - Wikipedia

   en.wikipedia.org/wiki/Cristobalite

   Specimen from California, US; size: 5.9 cm × 3.8 cm × 3.8 cm (2.3 in × 1.5 in × 1.5 in). Cristobalite (/ krɪˈstoʊbəˌlaɪt /) is a mineral polymorph of silica that is formed at very high temperatures. It has the same chemical formula as quartz, SiO 2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all ...