File:Chalcocite (latest Cretaceous to earliest Tertiary, 62-66 Ma; Butte Mining District, Montana, USA).jpg
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| Description |
English: Chalcocite from Montana, USA. (3.7 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 5600 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 sulfide minerals contain one or more sulfide anions (S-2). The sulfides are usually considered together with the arsenide minerals, the sulfarsenide minerals, and the telluride minerals. Many sulfides are economically significant, as they occur commonly in ores. The metals that combine with S-2 are mainly Fe, Cu, Ni, Ag, etc. Most sulfides have a metallic luster, are moderately soft, and are noticeably heavy for their size. These minerals will not form in the presence of free oxygen. Under an oxygen-rich atmosphere, sulfide minerals tend to chemically weather to various oxide and hydroxide minerals. Chalcocite is a significant copper ore mineral having the formula Cu2S - copper sulfide. It has a metallic luster, a dark gray to black color & streak, no obvious cleavage, is moderately heavy for its size, and is moderately soft (H = 2.5 to 3). Chalcocite is found with other copper minerals such as chalcopyrite. It usually forms in the near-surface, secondary enrichment zone at & below the water table, in areas having copper mineralization. It also occurs as a primary mineral in some hydrothermal veins. The above specimen is massive chalcocite from a hydrothermal vein in Montana's Butte Mining District. Butte was the top copper producer on Earth for many decades. In that area, hydrothermal veins have intruded and altered the Butte Quartz Monzonite (Butte Pluton, mid-Campanian Stage, late Late Cretaceous, 76 million years), a large intrusive igneous mass forming part of the Boulder Batholith. Copper sulfide-rich hydrothermal vein intrusion occurred at about 62 to 66 million years, around the time of the Cretaceous-Tertiary transition. Locality: Butte Mining District, Silver Bow County, southwestern Montana, USA Photo gallery of chalcocite: www.mindat.org/gallery.php?min=962 |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/18013910270/ |
| 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@N05/18013910270. It was reviewed on 8 March 2022 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 22:35, 8 March 2022 | | 978 × 579 (1.06 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/18013910270/ with UploadWizard |
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