Pyromorphite


Composition: Pb5(PO4)3Cl
Crystal System : Hexagonal
Colours: Green, yellow-green, brown, orange, grey
Lustre : Adamantine, greasy
Hardness (H) : 3.5-4.0
Specific Gravity (S.G) : 6.7-7.1
References:

Bartelke (1976)

Distribution

Very rare. First oxidation zone.

Occurrence

  • Supergene
  • 1st Oxidation Zone

Paragenetic and General Notes

Pyromorphite is very rare at Tsumeb. According to Pinch and Wilson (1977), needles and prisms to 20 mm were found, ranging from colourless, through green, brown and bright yellow. However, this claim was probably based on earlier and erroneous descriptions of specimens that are now known to be mimetite.

"Pyromorphite" was first recognised from the upper portion of the first oxidation zone by Schneider (1906) who described it as plentiful but, two years later, Maucher (1908) considered it rare in comparison with mimetite.  Several early "pyromorphites" from Tsumeb have now been shown to be mimetite crystals with a light secondary dusting of duftite.

Many alleged "Tsumeb pyromorphites" either turn out to be mimetite, or to have originated elsewhere.

Pufahl (1920) analysed several hundred mimetite specimens and found no phosphate, but a later spectrographic study of mimetite specimens in the Natural History Museum, London, found that a very few Tsumeb mimetites do have significant phosphate content (Mike Rumsey, personal communication to M.Southwood, October 2015).

Drescher (1926) was able to confirm pyromorphite from Tsumeb by spectrographic analysis, and Guillemin (1956) confirmed pyromorphite as tiny crystals on tsumebite by XRD analysis.

Gebhard (1999) notes that few "Tsumeb pyromorphites" have been verified analytically but that a single specimen with crystals to 5 mm is in the collection of Charles Key.

The following minerals are reported to form pseudomorphs after pyromorphite:  descloizite (rare, doubtful validity); tsumebite (rare, doubtful validity); vanadinite (rare, doubtful validity).