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  2. Porphyry (geology) - Wikipedia

    en.wikipedia.org/wiki/Porphyry_(geology)

    Porphyry (geology) Porphyry ( / ˈpɔːrfəri / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate -rich, generally aphanitic matrix or groundmass. In its non-geologic, traditional use, the term porphyry usually refers to the purple-red form of ...

  3. Amethyst - Wikipedia

    en.wikipedia.org/wiki/Amethyst

    Amethyst. Amethyst is a violet variety of quartz. The name comes from the Koine Greek αμέθυστος amethystos from α- a-, "not" and μεθύσκω ( Ancient Greek) methysko / μεθώ metho ( Modern Greek ), "intoxicate", a reference to the belief that the stone protected its owner from drunkenness. [ 1]

  4. Obsidian - Wikipedia

    en.wikipedia.org/wiki/Obsidian

    Obsidian is mineral -like, but not a true mineral because, as a glass, it is not crystalline; in addition, its composition is too variable to be classified as a mineral. It is sometimes classified as a mineraloid. [ 20] Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic.

  5. Topaz - Wikipedia

    en.wikipedia.org/wiki/Topaz

    Topaz is a silicate mineral made of aluminum and fluorine with the chemical formula Al 2 Si O 4 ( F, OH) 2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow-orange. [7]

  6. Lapis lazuli - Wikipedia

    en.wikipedia.org/wiki/Lapis_Lazuli

    A mixture of other minerals, often including pyrite. Lapis lazuli ( UK: / ˌlæpɪs ˈlæz ( j) ʊli, ˈlæʒʊ -, - ˌli /; US: / ˈlæz ( j) əli, ˈlæʒə -, - ˌli / ), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color.

  7. Pyrite - Wikipedia

    en.wikipedia.org/wiki/Pyrite

    Pyrite is the most common of sulfide minerals and is widespread in igneous, metamorphic, and sedimentary rocks. It is a common accessory mineral in igneous rocks, where it also occasionally occurs as larger masses arising from an immiscible sulfide phase in the original magma.

  8. Azurite - Wikipedia

    en.wikipedia.org/wiki/Azurite

    Azurite was known in the pre-classical ancient world. It was used in ancient Egypt as a pigment, obtained from mines in Sinai. Ancient Mesopotamian writers report the use of a special mortar and pestle for grinding it. It was also used in ancient Greece, for example on the Acropolis in Athens.

  9. Apatite - Wikipedia

    en.wikipedia.org/wiki/Apatite

    Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH −, F − and Cl − ion, respectively, in the crystal. The formula of the admixture of the three most common endmembers is written as Ca 10 ( PO 4) 6 (OH,F,Cl) 2, and the crystal unit cell formulae of the individual ...