Cornubite

cornubite

strashimitite

cornwallite

parnauite

Images

Formula: Cu5(AsO4)2(OH)4
Anhydrous arsenate containing hydroxyl, triclinic paramorph of cornwallite, which is monoclinic
Specific gravity: 4.64
Hardness: 4
Streak: Pale green
Colour: Apple green to dark green
Environments:

Hydrothermal environments

Cornubite is a rare secondary mineral in oxidised copper deposits. Near Reichenbach in the Oderwald, Germany, cornubite occurs in a silicified quartz vein (AM 70.1333).

At the type locality, Wheal Carpenter, Cornwall, England cornubite occurs in copper-tin-silver bearing hydrothermal veins, associated with cornwallite, chalcophyllite, olivenite, liroconite, chenevixite, clinoclase, pseudomalachite, bayldonite, parnauite, tyrolite, azurite, malachite, cuprite, chrysocolla and quartz (HOM).

At the San Rafael mine, Nye county, Nevada, USA, cornubite has been found with olivenite and strashimirite (R&M 85.6.517).

At Bou Azzer, Morocco cornubite has been found in quartz cavities together with scorodite (MinRec 38.5.

The Activity-pH diagram below was calculated at 298.2 K for some carbonates and copper arsenates for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of H2CO3 activity (MM 52.687).
stability AsO4, CO3.jpg

The mineral formulae are:
azurite: Cu3(CO3)2(OH)2
malachite: Cu2(CO3)(OH)2
olivenite: Cu2(AsO4)(OH)
cornubite: Cu5(AsO4)2(OH)4
clinoclase: Cu3(AsO4)(OH)3













The Activity-pH diagram below was calculated at 298.2 K for some arsenates and sulphates for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of SO42- activity (MM 52.689).
stability sulphates.jpg

The mineral formulae are:
chalcanthite: Cu(SO4).5H2O
antlerite: Cu2+3(SO4)(OH)4
brochantite: Cu4(SO4)(OH)6
olivenite: Cu2(AsO4)(OH)
cornubite: Cu5(AsO4)2(OH)4
clinoclase: Cu3(AsO4)(OH)3













Back to Minerals