File:Corundum (Pennsylvania, USA) 2.jpg
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| Description |
English: (~7.5 centimeters across at its widest)
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 5900 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. 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 The corundum crystal seen here is quite eroded, but its hexagonal crystal shape is still obvious. This specimen is large and dense - it weighs 3 pounds, 1 ounce. Locality: unrecorded / undisclosed site in Pennsylvania, USA Photo gallery of corundum: www.mindat.org/gallery.php?min=1136 |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/53197377406/ |
| 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@N05/53197377406. It was reviewed on 19 September 2023 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 17:25, 19 September 2023 | | 2,731 × 2,464 (4.4 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/53197377406/ with UploadWizard |
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