Pyromorphite Identification Guide

What Pyromorphite Looks Like

Pyromorphite (Pb5(PO4)3Cl, a lead chlorophosphate of the apatite group) is a secondary mineral of oxidized lead deposits. Colors are typically grass-green, yellow-green, and olive, but also yellow, orange, and brown. Luster is resinous to adamantine; crystals are translucent to subtransparent. The hallmark habit is hexagonal prisms, often short and barrel-shaped or rounded, frequently hollow or cavernous at the ends, and clustered in druses and crusts. It also occurs globular, botryoidal, and granular.

Step-by-Step Field ID Checklist

1. Note the color: bright grass-green to yellow-green is most typical and eye-catching.
2. Look at habit: small hexagonal prisms, often barrel-shaped or cavernous-ended, in crusts — very distinctive.
3. Check luster: resinous to greasy-adamantine, not glassy.
4. Heft it: surprisingly heavy (SG ~6.5–7.1) for a small specimen — the lead content shows.
5. Test hardness: 3.5–4, scratched by a knife.
6. Note the setting: oxidized zone of lead ore deposits, often with galena, cerussite, mimetite, and limonite.

Key Diagnostic Tests

• Specific gravity: ~6.5–7.1, very heavy — a strong clue given its modest hardness.
• Hardness: 3.5–4 (Mohs).
• Streak: white to yellowish-white.
• Luster: resinous to adamantine.
• Crystal habit: barrel-shaped/cavernous hexagonal prisms.
• Solubility: dissolves in nitric acid; fuses easily (the name means 'fire-form' from the globule it forms on cooling after melting).

Common Look-Alikes and How to Tell Them Apart

• Mimetite (Pb5(AsO4)3Cl): nearly identical in appearance and habit — the arsenate analog. They are often indistinguishable in the field; mimetite tends more yellow-brown and rounded, and chemical/lab tests separate As from P. Vanadinite (the vanadate analog) is usually brighter red-orange.
• Apatite: same crystal structure and green color possible, but apatite is much lighter (SG ~3.2) and harder (5). Pyromorphite's heft and softness separate it.
• Olivenite/green secondary copper minerals: copper minerals (malachite, etc.) are far lighter and fizz or differ in habit; malachite is fibrous/banded and effervesces in acid.
• Green prehnite/epidote: harder, glassy, much lighter, and not in lead-ore settings.

Where Pyromorphite Is Found

Look in the oxidized (weathered) zones of lead deposits. Famous localities include the Bunker Hill Mine (Idaho, USA), Bad Ems and the Black Forest (Germany), Cornwall and Cumbria (England), Les Farges (France), and Guangxi (China), which produces superb bright-green crystals. Associations include galena, cerussite, anglesite, mimetite, and iron oxides.