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2. 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 ...

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

4. Rutilated quartz - Wikipedia

   en.wikipedia.org/wiki/Rutilated_quartz

   Rutilated quartz used as a gemstone. Rutilated quartz is a variety of quartz which contains acicular (needle-like) inclusions of rutile. [1] It is used for gemstones. These inclusions mostly look golden, but they also can appear silver, copper red or black. The inclusions may be distributed randomly or in bundles, which sometimes are arranged ...

5. 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.

6. Llanite - Wikipedia

   en.wikipedia.org/wiki/Llanite

   Llanite. Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangeish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals. Llanite comes from a hypabyssal porphyritic rhyolite dike that intrudes Precambrian ...

7. Tiger's eye - Wikipedia

   en.wikipedia.org/wiki/Tiger's_eye

   Tiger's eye (also called tiger eye) is a chatoyant gemstone that is usually a metamorphic rock with a golden to red-brown colour and a silky lustre.As members of the quartz group, tiger's eye and the related blue-coloured mineral hawk's eye gain their silky, lustrous appearance from the parallel intergrowth of quartz crystals and altered amphibole fibres that have mostly turned into limonite.