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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. 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 ...

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. Gemstone - Wikipedia

   en.wikipedia.org/wiki/Gemstone

   Gemstone. Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or ...

7. 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. The style of termination at ...