Aragonite (Tazouta, Middle Atlas Mountains, Morocco) 7 : 無料・フリー素材/写真
Aragonite (Tazouta, Middle Atlas Mountains, Morocco) 7 / 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 | Aragonite from Morocco.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 carbonate minerals all contain one or more carbonate (CO3-2) anions.Aragonite has the same chemistry as calcite - it is calcium carbonate (CaCO3). However, aragonite has a different molecular structure - the atoms are packed differently. Different minerals having the same chemical formula are called "polymorphs" (another good example is graphite and diamond - both are carbon, C).Unlike calcite, aragonite forms crystals in the orthorhombic class. Many aragonite crystals are acicular (needle-like) or pseudohexagonal. The latter is the result of six orthorhombic prisms growing parallel to each other. The sample seen here is a radiating cluster of pseudohexagonal, cyclic-twinned aragonite masses.Aragonite is slightly harder than calcite, at H=3.5 to 4, occurs in many colors, and easily bubbles in acid. Aragonite is a little bit heavier than calcite, due to closer packing of atoms.Most modern seashells and coral skeletons are composed of the aragonite. Whitish-colored lime sand beaches in the world are aragonitic. Occasionally, "whitings" are seen in shallow, warm ocean environments. Whitings (cloudy, milky seawater) turn out to have numerous tiny, hair-like needles of aragonite. In the rock record, aragonitic or aragonite-rich sediments convert to calcite over time. Cenozoic-aged carbonate sedimentary rocks are often aragonitic. Mesozoic- and Paleozoic-aged carbonates are almost always calcitic. Many ancient fossils have had their aragonitic shells dissolved away. Ancient shells that were originally calcitic are often still well preserved.Locality: Tazouta, southeast of Sefrou & southeast of Fez, Middle Atlas Mountains, northern Morocco-----------------Photo gallery of aragonite:www.mindat.org/gallery.php?min=307 |
| 撮影日 | 2025-01-07 10:45:26 |
| 撮影者 | James St. John |
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