Amethyst (faceted) (Sebago Pluton, Early Permian, ~293 Ma; Deer Hill, north of Stow, Maine, USA) 8 : 無料・フリー素材/写真
Amethyst (faceted) (Sebago Pluton, Early Permian, ~293 Ma; Deer Hill, north of Stow, Maine, USA) 8 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Bicolored amethyst gemstones from Maine, USA. (Left: 14.66 carats; right: 17.23 carats; Maine Mineral & Gem Museum collection, Bethel, Maine, USA)A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 6100 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.The silicates are the most abundant and chemically complex group of minerals. All silicates have silica as the basis for their chemistry. "Silica" refers to SiO2 chemistry. The fundamental molecular unit of silica is one small silicon atom surrounded by four large oxygen atoms in the shape of a triangular pyramid - this is the silica tetrahedron - SiO4. Each oxygen atom is shared by two silicon atoms, so only half of the four oxygens "belong" to each silicon. The resulting formula for silica is thus SiO2, not SiO4. The simplest & most abundant silicate mineral in the Earth's crust is quartz (SiO2). All other silicates have silica + impurities. Many silicates have a significant percentage of aluminum (the aluminosilicates).Quartz (silicon dioxide/silica - SiO2) is the most common mineral in the Earth's crust. It is composed of the two most abundant elements in the crust - oxygen and silicon. It has a glassy, nonmetallic luster, is commonly clearish to whitish to grayish in color, has a white streak, is quite hard (H≡7), forms hexagonal crystals, has no cleavage, and has conchoidal fracture. Quartz can be any color: clear, white, gray, black, brown, pink, red, purple, blue, green, orange, etc.Purple quartz is called amethyst. The coloring agent for amethyst is not agreed upon. Some workers say that it is due to Fe+4 impurity, some say the impurity is Fe+3, and others say it is Mn.---------------Exhibit info.MAINE AMETHYSTThere are over a dozen locations in Maine where amethyst is reported to occur, but few have produced significant quantities of this purple mineral.Notably, these include the quarries / pits around Colton and Deer Hill in Stow, all pegmatite deposits, and the Saltman Prospect in Sweden, a hydrothermal deposit.AMETHYST QUICK FACTSAmethyst is the purple variety of the mineral quartz.Mineral formula for quartz: SiO2.The name is derived from the Greek a-methystos, meaning "not drunk", as it was believed that amethyst prevented intoxication.Amethyst is the February birthstone.Amethyst gets its purple color from trace amounts of iron in the quartz structure.After tourmaline, amethyst is the second most popular gemstone from Maine.In Maine, amethyst is found in granitic pegmatites and hydrothermal deposits.---------------Geologic unit: Deer Hill Pegmatite, Sebago Pluton, Oxford Pegmatite Field, early Early Permian, ~293 MaLocality: Deer Hill, north of the town of Stow, southwestern Maine, USA---------------Locality info.:www.mindat.org/loc-4613.html---------------Photo galleries of quartz and amethyst:www.mindat.org/gallery.php?min=3337andwww.mindat.org/gallery.php?min=198 |
| 撮影日 | 2025-04-26 14:13:28 |
| 撮影者 | James St. John |
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