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Pyromorphite



Pyromorphite

Yellow pyromorphite from Australia
General
CategoryMineral
Chemical formulaPb5(PO4)3Cl
Identification
Molecular Weight1,356.37 gm
ColorColorless, Green, Yellow, etc...
Crystal habitmassive to crystaline
Crystal systemHexagonal
CleavageImperfect- [1011]
FractureBrittle
TenacityBrittle
Mohs Scale hardness3.5-4
Lustervitreous
Ultraviolet fluorescenceNone
StreakWhite
Density7.109 g/cm3
DiaphaneityTransparent to opaque

Pyromorphite is a mineral species composed of lead chlorophosphate: Pb5(PO4)3Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. Crystals with a barrel-like curvature are not uncommon. Globular and reniform masses are also found. It is part of a series with two other minerals: mimetite (Pb5(AsO4)3Cl) and vanadinite (Pb5(VO4)3Cl), the resemblance in external characters is so close that, as a rule, it is only possible to distinguish between them by chemical tests.

They were formerly confused under the names green lead ore and brown lead ore (German, Grünbleierz and Braunbleierz). The phosphate was first distinguished chemically by M. H. Kiaproth in 1784, and it was named pyromorphite by J. F. L. Hausmann in 1813.  

The color of the mineral is usually some bright shade of green, yellow or brown, and the luster is resinous. The hardness is 3, and the specific gravity 6.5 - 7.1. Owing to isomorphous replacement of the phosphorus by arsenic there may be a gradual passage from pyromorphite to mimetite. Varieties containing calcium isomorphously replacing lead are lower in density (specific gravity 5.9 - 6.5) and usually lighter in color; they bear the names polysphaerite (because of the globular form), miesite from Mies in Bohemia, nussierite from Nuizière, Chénelette, near Beaujeu, Rhône, France, and cherokine from Cherokee County in Georgia.

See also

References

  • This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Pyromorphite". A list of authors is available in Wikipedia.
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