File:Corundum (Soutpansberg Range area, South Africa) 2.jpg
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English: 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 5700 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 oxide minerals all contain one or more oxide anions (O-2). The oxide minerals include species that are hydroxy-oxides. The hydroxide minerals (those with one or more OH-) are usually considered together with the oxides. Many sulfide minerals are not stable in Earth-surface conditions. In the presence of oxygen and moisture, sulfide minerals tend to tarnish or alter to oxides and hydroxy-oxides. All except the most inert elements (such as the platinum-group elements and gold and noble gases) readily form oxides. Gold oxide forms only under special conditions. Corundum is aluminum oxide - Al2O3. At H≡9, it is the hardest common mineral, apart from diamond. Corundum forms hexagonal crystals, which is evident even in many river-worn specimens. The hexagonal columns of corundum typically have well-developed flat tops & bottoms. These flat ends are not cleavage planes - corundum has no cleavage. The cleavage-looking flat tops & bottoms of corundum are called partings (pseudocleavage). Additional breakages will not be along planar surfaces. Striations may be visible on the flat ends (click once or twice on the photo to zoom in on the specimen at right). The color of corundum is variable - it can be any color, including plaid patterns. If transparent and relatively fracture-free & inclusion-free, corundum is said to be of gem-quality, and the color determines the name of the gem. deep red = ruby blue = sapphire pale red = sapphire pale green = sapphire purple = sapphire yellow = sapphire Locality: unrecorded / undisclosed site in the Soutpansberg Range area, Vhembe District, Limpopo Province, northeastern South Africa Photo gallery of corundum: www.mindat.org/gallery.php?min=1136 |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/52019569406/ |
| 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@N05/52019569406. It was reviewed on 21 April 2022 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 14:17, 21 April 2022 | | 1,887 × 1,059 (1.25 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/52019569406/ with UploadWizard |
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