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Category Phosphate minerals
(repeating unit)
Strunz classification 8.BL.05
Dana classification
Crystal system Trigonal
Crystal class Ditrigonal pyramidal (3/m)
(same H-M symbol)
Space group R3m
Unit cell a = 7.3065(5) Å,
c = 16.897(2) Å;
V = 781.2 Å³; Z = 3
Formula mass 667.82 g/mol
Color Brown to light yellowish brown, pale yellow, yellowish green to dark green
Crystal habit Crystals pseudocubic rhombohedral with prominent {1011}. Commonly in crusts and massive
Cleavage Perfect on {0001}
Mohs scale hardness 3.5 - 4.5
Luster Vitreous, resinous
Diaphaneity transparent
Specific gravity 4.295 (measured), 4.31 (calculated)
Optical properties uniaxial (-), may appear anomalously biaxial
Refractive index nω = 1.930 nε = 1.930 n = 1.93 - 1.96
Birefringence δ = 0.000
Other characteristics Readily soluble in warm HCl
References [1][2][3][4][5]

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 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]