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www.mineralgallery.co.za Minerals P-T |
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Pyromorphite |
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Name
Pyromorphite
Chemistry
Pb5(PO4)3Cl.
Uses
A minor ore of lead..
Color-
Various shades of green and brown: also orange-yellow aand red: rarely colourless:
Hardness
3.5-4
Specific gravity
6.5-7.1.
Crystal system:
Hexagonal.
Accompanied by:
Associated with other lead minerals and sometimes in zoned crystals with the outer parts tending towards mimetite.
Fracture
Uneven to subconchoidal fracture.
Luster
Resinous to subadamantine.
Cleavage
Poor, prismatic cleavage:
Streak
White or yellowish-white
Similar to:
Pyromorphite is found as a supergene mineral in the upper oxidised parts of lead deposits in association with cerussite, limonite, smithsonite and anglesite
Pyromorphite has a widespread distribution and is found in many lead mines world wide.
It is also a minor ore mineral of lead.
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.
