File:Gold and quartz (Placerville, California, USA) (17207487751).jpg
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Summary
[edit]DescriptionGold and quartz (Placerville, California, USA) (17207487751).jpg |
Gold and quartz from California, USA. (SDSMT 5101, South Dakota School of Mines and Technology Museum of Geology, Rapid City, South Dakota, USA) A mineral is a naturally-occurring, solid, inorganic, crystalline substrance 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 4900 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. Elements are fundamental substances of matter - matter that is composed of the same types of atoms. At present, 118 elements are known (four of them are still unnamed). Of these, 98 occur naturally on Earth (hydrogen to californium). Most of these occur in rocks & minerals, although some occur in very small, trace amounts. Only some elements occur in their native elemental state as minerals. To find a native element in nature, it must be relatively non-reactive and there must be some concentration process. Metallic, semimetallic (metalloid), and nonmetallic elements are known in their native state as minerals. Gold (Au) is the most prestigious metal known, but it's not the most valuable. Gold is the only metal that has a deep, rich, metallic yellow color. Almost all other metals are silvery-colored. Gold is very rare in crustal rocks - it averages about 5 ppb (parts per billion). Where gold has been concentrated, it occurs as wires, dendritic crystals, twisted sheets, octahedral crystals, and variably-shaped nuggets. It most commonly occurs in hydrothermal quartz veins, disseminated in some contact- & hydrothermal-metamorphic rocks, and in placer deposits. Placers are concentrations of heavy minerals in stream gravels or in cracks on bedrock-floored streams. Gold has a high specific gravity (about 19), so it easily accumulates in placer deposits. Its high density allows prospectors to readily collect placer gold by panning. In addition to its high density, gold has a high melting point (over 1000º C). Gold is also relatively soft - about 2.5 to 3 on the Mohs Hardness Scale. The use of pure gold or high-purity gold in jewelry is not desirable as it easily gets scratched. The addition of other metals to gold to increase the hardness also alters the unique color of gold. Gold jewelry made & sold in America doesn’t have the gorgeous rich color of high-purity gold. Locality: Placerville, California, USA |
Date | |
Source | Gold and quartz (Placerville, California, USA) |
Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/17207487751. It was reviewed on 3 May 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
3 May 2015
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current | 20:50, 3 May 2015 | ![]() | 1,749 × 858 (1.09 MB) | Natuur12 (talk | contribs) | Transferred from Flickr via Flickr2Commons |
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ISO speed rating | 400 |
Date and time of data generation | 11:54, 18 August 2010 |
Lens focal length | 200 mm |
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Bits per component |
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Horizontal resolution | 300 dpi |
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File change date and time | 00:54, 20 April 2015 |
Y and C positioning | Co-sited |
Exposure Program | Not defined |
Exif version | 2.21 |
Date and time of digitizing | 11:54, 18 August 2010 |
Meaning of each component |
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APEX exposure bias | 0 |
Maximum land aperture | 5 APEX (f/5.66) |
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Focal length in 35 mm film | 300 mm |
Scene capture type | Standard |
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Date metadata was last modified | 20:54, 19 April 2015 |
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