Pyromorphite

Pyromorphite is a lead chlorophosphate mineral, Pb5(PO4)3Cl, belonging to the apatite group. It is best known for its attractive green, yellow-green, and brown crystals, which often take a distinctive barrel-shaped or hexagonal prismatic form.

Its name comes from the Greek words for fire and form, referring to the way a melted globule of the mineral crystallizes into a faceted shape as it cools.

Pyromorphite forms a series with mimetite (the arsenate equivalent) and vanadinite, and the three can be difficult to distinguish without chemical testing. It is a popular collector mineral and a minor ore of lead.

Pyromorphite is a secondary mineral that forms in the oxidized zones of lead ore deposits. It develops when phosphate-bearing solutions react with primary lead minerals such as galena that have been altered by weathering.

It typically occurs as crusts, druses, and clusters of small crystals lining cavities in gossan and weathered ore veins, often associated with cerussite, mimetite, and limonite.

Notable localities include the Bunker Hill mine (Idaho), Daoping (China), Bad Ems and the Eifel (Germany), Cornwall (England), and the Les Farges mine (France), which has produced exceptional orange and green crystals.

Pyromorphite is recognized by its green to yellow-green or brown color, resinous to adamantine luster, and characteristic barrel-shaped hexagonal crystals, often grouped in clusters. It has a hardness of 3.5 to 4 and is notably heavy due to its lead content.

Its white streak and crystal habit help, but distinguishing it from mimetite and vanadinite by eye is difficult since they share the same structure and habits.

Mimetite (arsenate) tends toward yellow and rounded forms, while vanadinite is typically deeper red; reliable separation usually requires chemical or instrumental analysis.

Pyromorphite is a minor ore of lead where it occurs in quantity, though it is not a major source compared with galena.

It has gained interest in environmental science because lead readily converts to stable pyromorphite in the presence of phosphate, a reaction used to immobilize lead contamination in polluted soils and remediate toxic sites.

For collectors, brightly colored crystalline pyromorphite, especially the vivid green Chinese specimens and orange French material, is highly desirable. Because it contains lead, specimens should be handled with care.