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Mimetite
From Wikipedia, the free encyclopedia
| Mimetite | |
|---|---|
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| General | |
| Category | Mineral |
| Chemical formula | Pb5(AsO4)3Cl lead chloro-arsenate |
| Identification | |
| Color | Yellow, Brown, Orange, Red, White |
| Crystal habit | Reniform, botryoidal, globular, prismatic |
| Crystal system | Hexagonal |
| Cleavage | [1011] Imperfect |
| Fracture | Brittle, conchoidal |
| Mohs Scale hardness | 3.5 - 4 |
| Luster | Resinous, adamantine |
| Refractive index | 2.129 - 2.144 |
| Streak | White |
| Specific gravity | 7.1 - 7.24 |
| Diaphaneity | Subtransparent to translucent |
Mimetite, whose name derives from the Greek mimethes, meaning "imitator", is an arsenate mineral which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name is a reference to mimetite's resemblance to the mineral pyromorphite. This resemblance is not coincidental, as mimetite forms a mineral series with pyromorphite (Pb5(PO4)3Cl) and with vanadinite (Pb5(VO4)3Cl). The most notable occurrences are Mapimi, Durango, Mexico and Tsumeb, Namibia.
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Industrially, mimetite is a minor ore of lead, especially when found in relatively large quantities. The chief use of mimetite is as a collector's specimen, often creating very attractive botryoidal crusts on the surface of the specimen. Though mimetite is also found in prismatic crystal forms, it is not used as a gemstone due to its softness. The best of these prismatic forms have been found in Johanngeorgenstadt in Saxony and Wheal Unity in Cornwall, England.
Mimetite is found in association with lead and arsenic minerals, including those minerals with which it forms a series. Some associated minerals include:
- galena, PbS
- pyromorphite, Pb5(PO4)3Cl
- vanadinite, Pb5(VO4)3Cl
- wulfenite, PbMoO4
- smithsonite, ZnCO3
- calcite, CaCO3
- bellite
Alternative names of mimetite include arsenopyromorphite, mimetesite, and prixite. Campylite is the name for a variety with barrel shaped crystals of a brownish-red or orange-yellow color and containing a considerable proportion of phosphoric acid.
Useful information pertaining to the field identification of mimetite include its habit, color, and high density. However, this mineral's similarity to pyromorphite can be problematic, especially since these minerals are known to share colors. Pyromorphite is typically green, and mimetite is typically yellow, but specimens of each are known in the other's colors. As a result, some identification may require lab analysis.