Pyromorphite

Pyromorphite from Broken Hill, New South Wales, Australia. Photograph taken at the Natural History Museum, London. © Aram Dulyan

Chemical Formula: Pb5(PO4)3Cl
Name Origin: From the Greek pyr – “fire” and morfe – “form” in allusion the recrystallization reaction of the molten mineral.

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.

History

Authors : HAUSMANN
Discovery date : 1813

Optical properties

Optical and misc. Properties : Transparent  –   Translucide  –   Fragile, cassant  –   Luminescent, fluorescent
Refractive Index : from 2,04 to 2,05

Physical properties

Hardness: from 3,50 to 4,00
Density : 7,04
Color : green; yellow; orange; brown; grey; colorless; white; red yellow; yellowish brown; purplish brown
Luster: sub-adamantine; resinous; greasy
Streak : white; grey; yellowish
Break: irregular; sub-conchoidal
Cleavage: yes

Photos:

Pyromorphite Mina San Andrés, Geoda Realces, Villaviciosa de Córdoba, Espiel, Córdoba  Spain (10/11-1997) Specimen size: 3.7 × 2.5 × 1 cm = 1.5” × 1.0” × 0.4” Main crystal size: 0.3 × 0.3 cm = 0.1” × 0.1” © Fabre Minerals
Pyromorphite Rosenberg Mine, Braubach, Bad Ems District, Lahn valley, Rhineland-Palatinate, Germany Size: 6.0 x 2.5 x 1.6 cm (miniature) © danweinrich
Pyromorphite Mine des Farges, Ussel, Corrèze  France Specimen size: 3 × 2.5 × 1.4 cm = 1.2” × 1.0” × 0.6” © Fabre Minerals
Pyromorphite Bunker Hill Mine, Kellogg, Coeur d’Alene District, Shoshone Co., Idaho, USA Size: 2.0 x 2.0 x 1.2 cm (thumbnail) © danweinrich
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