Corkite

Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. Corkite is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite.

Corkite
Corkite-Goethite.jpg
Corkite on a goethite matrix
General
CategoryPhosphate minerals
Formula
(repeating unit)
PbFe3[(OH)6:SO4:PO4]
Strunz classification8.BL.05
Dana classification43.4.1.2
Crystal systemTrigonal
Crystal classDitrigonal pyramidal (3/m)
(same H-M symbol)
Space groupR3m
Unit cella = 7.3065(5) Å,
c = 16.897(2) Å;
V = 781.2 Å³; Z = 3
Identification
Formula mass667.82 g/mol
ColorBrown to light yellowish brown, pale yellow, yellowish green to dark green
Crystal habitCrystals pseudocubic rhombohedral with prominent {1011}. Commonly in crusts and massive
CleavagePerfect on {0001}
Mohs scale hardness3.5 - 4.5
LusterVitreous, resinous
Diaphaneitytransparent
Specific gravity4.295 (measured), 4.31 (calculated)
Optical propertiesuniaxial (-), may appear anomalously biaxial
Refractive indexnω = 1.930 nε = 1.930 n = 1.93 - 1.96
Birefringenceδ = 0.000
Other characteristicsReadily soluble in warm HCl
References[1][2][3][4][5]

Corkite is named after County Cork, Ireland; the location where the first notable amount was discovered in 1869.[2] Like many of the other minerals in the beudantite group, corkite is a relatively uncommon, secondary mineral that occurs in oxidation zones near hydrothermal base metal deposits.[2] It occurs associated with pyromorphite, malachite, plumbojarosite, limonite and quartz.[5]

ReferencesEdit