File:Milky quartz (Diamond Hill, Ashaway Village, Hopkinton, Rhode Island, USA) (34560451746).jpg
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Summary[edit]
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Quartz from Rhode Island, 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 5100 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. The Rhode Island milky quartz shown above comes from a site where amethyst (= purple quartz) is frequently found perched atop milky quartz. Research has shown that the two quartz types precipitated at disparate times, but both have an epithermal meteoric origin - the silica precipitated from fluids ultimately derived from rainwater. The quartz apparently formed along conduits in quartzites of the Plainfield Formation (Proterozoic). Locality: excavation at Diamond Hill, Ashaway Village, south of Hopkinton, southwestern Washington County, southwestern Rhode Island, USA Photo gallery of quartz: <a href="http://www.mindat.org/gallery.php?min=3337" rel="nofollow">www.mindat.org/gallery.php?min=3337</a> Site-specific info. synthesized from: Rakovan et al. (1995) - Amethyst on milky quartz from Hopkinton, Rhode Island. Mineralogical Record 26(2): 83-89. |
| Date | |
| Source | Milky quartz (Diamond Hill, Ashaway Village, Hopkinton, Rhode Island, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/34560451746 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 02:05, 5 December 2019 | | 1,781 × 3,143 (3.31 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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