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  2. Quartz - Wikipedia

    en.wikipedia.org/wiki/Quartz

    Quartz is the mineral defining the value of 7 on the Mohs scale of hardness, a qualitative scratch method for determining the hardness of a ... Some can also be black ...

  3. Smoky quartz - Wikipedia

    en.wikipedia.org/wiki/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 the ...

  4. 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 ...

  5. Chlorite group - Wikipedia

    en.wikipedia.org/wiki/Chlorite_group

    Quartz crystal with chlorite inclusions from Minas Gerais, Brazil (size: 4.2 × 3.9 × 3.3 cm) Chlorite is a common mineral, found in metamorphic, igneous, and sedimentary rocks. It is an important rock-forming mineral in low- to medium-grade metamorphic rock formed by metamorphism of mafic or pelitic rock. [9]

  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. List of gemstones by species - Wikipedia

    en.wikipedia.org/wiki/List_of_gemstones_by_species

    Main page; Contents; Current events; Random article; About Wikipedia; Contact us; Donate; Help; Learn to edit; Community portal; Recent changes; Upload file

  8. Carbonado - Wikipedia

    en.wikipedia.org/wiki/Carbonado

    Carbonado, commonly known as black diamond, is one of the toughest forms of natural diamond. It is an impure, high-density, micro-porous form of polycrystalline diamond consisting of diamond, graphite , and amorphous carbon , with minor crystalline precipitates filling pores and occasional reduced metal inclusions. [ 1 ]

  9. Quartzite - Wikipedia

    en.wikipedia.org/wiki/Quartzite

    Quartzite. Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone. [1][2] Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and ...

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