Philipsbornite

minerals

gibbsite

stolzite

crocoite

Formula: PbAl3(AsO4)(AsO3OH)(OH)6
Arsenate containing hydroxyl, crandallite group
Specific gravity: 4.33
Hardness: 4½
Colour: Colourless, white, yellow, green or grey, pale blue
Environments

Hydrothermal environments

Philipsbornite is a rare secondary supergene mineral in the oxidised zone of hydrothermal polymetallic mineral deposits (HOM).

Localities

At the type locality, the Red Lead Mine, Dundas mineral field, Zeehan district, West Coast municipality, Tasmania, Australia, philipsbornite occurs as massive to earthy crusts, composed of fine-grained aggregates, associated with crocoite, hidalgoite and gorceixite (AM 67.859, AJM 12.2.84, HOM).

At Tsumeb, Namibia, philipsbornite is associated with azurite, tsumcorite, bayldonite, malachite, hematite and quartz (HOM).

At Wheal Unity, Gwennap, Cornwall, England, England, UK, philipsbornite has been identified on a specimen as drusy crusts of minute trigonal crystals to 0.05 mm (M&M 25.37).

At the Cligga mine, Perranzabuloe, Cornwall, England, UK, an assemblage of lead-bearing minerals is reported surrrounding small masses of partially oxidised galena in high temperature tin-tungsten veins. The assemblage includes philipsbornite, and carminite, pyromorphite, mimetite, plumbogummite, raspite and stolzite (M&M 34.29-32).

Alteration

philipsbornite, H+ and H2O to Pb2+, gibbsite and H3AsO4
PbAl3(AsO4)(AsO3OH)(OH)6(s) + 2H+(aq) +3H2O(l) = Pb2+(aq) + 3Al(OH)3(s) + 2H3AsO4(aq)
(LMW p269)

The Activity-pH diagram below was calculated at 298.2 K for the main Cu2+ and Pb2+ arsenate minerals. Boundaries are calculated for constant activities (roughly equivalent to concentrations) of Pb2+ and Cl- ions in solution, over a range of values of pH and of Cu2+ activity. Higher chloride activites make the stability fields of bayldonite and duftite vanish, with respect to the encroachment of that of mimetite (LMW p269).
stability Cu Pb.jpg

The arsenate mineral formulae are:
philipsbornite PbAl3(AsO4)(AsO3OH)(OH)6
mimetite Pb5(AsO4)3Cl
duftite PbCu(AsO4)(OH)
bayldonite Cu3PbO(AsO3OH)2(OH)2
olivenite Cu2(AsO4)(OH)
cornwallite Cu5(AsO4)2(OH)4
clinoclase Cu3(AsO4)(OH)3










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