Pyromorphite represents a mineral series containing lead chlorophosphate, Pb5 (PO4) 3Cl, available for mining in abundance as a minor source of lead ore. In the zone of oxidized lead deposits, you can see that this mineral occurs with Liminite, Cerussite and Galena in globular mass crystals that are barrel shaped and brightly colored. The crystals of this mineral appear like hexagonal prism that terminates in basal planes that often blend with fine hexagonal pyramid faces. Sometimes they exhibit a curvature that has a barrel-like configuration. This mineral is closely associated in a series with mimetite, which has a formula Pb5 (AsO4) 3Cl and the mineral vanadinite whose formula is Pb5 (VO4) 3Cl. On the face of it they are so identical and can be distinguished apart only using chemical tests. It also has a close resemblance to Apatite in both properties and structure.
Normally you find that this mineral is mined in Bohemia, Nuiziere, Rhone, in France, Chenelette close to Beauieu and in the US in the Cherokee County of Georgia.
Derivation of Name
Earlier confused as “brown lead ore” or “green lead ore” it was in 1784 that M. H. Klaproth chemically identified this phosphate mineral, which J. F. L. Hausmann later on in 1813 named pyromorphite. As regards the derivation of the name it is supposed to have originated from a Greek word “pyr” for fire and “morfe” for form.
Pb5 (PO4) 3Cl
This mineral usually appears in shades of bright green, yellow or brown and has a resinous luster and the hardness of 3.5 to 4 and a density of 6.5 to 7.1. Due to Arsenic replacing Phosphorus in an Isomorphic replacement process, this mineral can slowly become Mimetite.
The color is dark green, Yellow-Orange, Yellow, Green, Reddish Orange, Grayish, Yellow Brown or colorless.
Hexagonal - Dipyramidal
Seldom on (1122)
The density can range from 7.04 to 7.14 (measured/calculated) or 5.9 to 6.5 depending on the Calcium and Lead deposits.
Hardness (Mohs scale)
3.5 - 4