Beudantite

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Beudantite
Beudantite-ea12a.jpg
Large brown crystals of Beudantite.
General
Category Arsenate minerals
Formula
(repeating unit)
PbFe3(OH)6SO4AsO4
Strunz classification 08.BL.10
Dana classification 43.4.1.1
Crystal symmetry Trigonal 3 2/m
Unit cell a = 7.32 Å, c = 17.02 Å;
Z = 3
Identification
Color black, dark green, brown, yellowish, red, greenish yellow, brown
Crystal habit tabular, acute rhombohedral, pseudo-cubic, pseudo-cuboctahedral
Crystal system Trigonal Hexagonal Scalenohedral
Cleavage distinct; good on {0001}
Mohs scale hardness 3.5-4.5
Luster vitreous, resinous
Streak grayish yellow to green
Diaphaneity transparent, translucent
Specific gravity 4.48
Optical properties Uniaxial (-)
Refractive index nω = 1.957 nε = 1.943
Birefringence δ = 0.014
Pleochroism visible
Other characteristics Soluble in HCl
References [1][2][3]

Beudandite is a secondary mineral occurring in the oxidized zones of polymetallic deposits.[3] It is a lead, iron, arsenate, sulfate with endmember formula: PbFe3(OH)6SO4AsO4.

Beudantite is in a subgroup of the alunite group. It is the arsenate analogue of the phosphate corkite. Beudantite also forms a solid-solution with segnitite and plumbojarosite.[1]

It crystallizes in the trigonal crystal system and shows a variety of crystal habits including tabular, acute rhombohedral, pseudo-cubic and pseudo-cuboctahedral.

It occurs in association with carminite, scorodite, mimetite, dussertite, arseniosiderite, pharmacosiderite, olivenite, bayldonite, duftite, anglesite, cerussite and azurite.[3]

Discovery[edit]

Beudantite was first described in 1826 for an occurrence in the Louise Mine, Wied Iron Spar District, Westerwald, Rhineland-Palatinate, Germany. It was named after French mineralogist François Sulpice Beudant (1787–1850).[1]

References[edit]