Anhydrous arsenate containing hydroxyl, adelite - descloizite group, forms series with conichalcite and with mottramite.
Specific gravity: 6.12
Streak: Pale green, white
Colour: Olive-green, grey-green; light apple-green in transmitted light.
Duftite is a secondary mineral that occurs in the oxidised zone of
hydrothermal metal ore deposits. At the type
locality it is associated with azurite (Mindat).
At Arm O'Grain, Cumbria, England, mottramite and duftite are almost indistinguishable, due to much arsenate substitution for vanadate in mottramite. It occurs with mimetite (JRS 9.48).
At Driggith and Sandbed Mines, Cumbria, England, duftite is associated with mottramite (JRS 9.20).
At Short Grain, Cumbria, England, duftite occurs rarely in vugs in quartz and baryte, commonly overgrown by mimetite (JRS 12.53).
At the San Rafael Mine, Nevada, USA, duftite occurs in pods of limonite associated with adamite, segnitite, wulfenite and mimetite (R&M 88.6.517-518).
duftite (s) and H2CO3 (aq) to cerussite (s), malachite (s), H2AsO4- (aq) and H+ (aq)
2PbCuAsO4(OH) + 3H2CO3 ⇌ 2PbCO3 + Cu2CO3(OH)2 + 2H2AsO4- + 2H+
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).
The arsenate mineral formulae are:
Back to Minerals