Pyromorphite

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Pyromorphite
Pyromorphite from Australia.jpg
Yellow pyromorphite from Australia
General
Category Phosphate mineral
Apatite group
Formula
(repeating unit)
Pb5(PO4)3Cl
Strunz classification 08.BN.05
Identification
Color Dark grass-green, green, yellow, yellow-orange, reddish orange, yellow-brown, brown, tan, grayish, may be colorless
Crystal habit Prismatic to acicular crysals, globular to reniform
Crystal system Hexagonal - Dipyramidal H-M Symbol (6/m) Space Group: P 63/m
Twinning Rarely on {1122}
Cleavage Imperfect- [1011]
Fracture Uneven to sub-conchoidal
Tenacity Brittle
Mohs scale hardness 3.5-4
Luster Resinous to subadamantine
Streak White
Diaphaneity Transparent to translucent
Specific gravity 7.04 measured, 7.14 calculated
Optical properties Uniaxial (-) May be anomalously biaxial -
Refractive index nω = 2.058 nε = 2.048
Birefringence δ = 0.010
Pleochroism Weak
Ultraviolet fluorescence May fluoresce yellow to orange under LW and SW UV
Other characteristics Piezoelectric if biaxial
References [1][2][3]

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. Klaproth in 1784, and it was named pyromorphite by J. F. L. Hausmann in 1813. The name is derived from the Greek for pyr (fire) and morfe (form) due to its crystallization behavior after being melted.[2]

Cylindrical yellow green pyromorphite crystals, Chihuahua, Mexico

Properties and isomorphism[edit]

The color of the mineral is usually some bright shade of green, yellow or brown, and the luster is resinous. The hardness is 3.5 to 4, 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.

Right frame 
Pyromorphite3d.jpg
Small specimen of Pyromorphite from China

See also[edit]

References[edit]