Beudantite

Beudantite
240px 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

Beudandite is a secondary mineral occurring in the oxidized zones of polymetallic deposits. 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.

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.

Discovery

Beudantite was first described in 1826 for an occurrence in the Louise Mine, Wied Iron Spar District, Westerwald, Rhineland-Palatinate, Germany. It was named by Armand Lévy after his fellow Frenchman and mineralogist François Sulpice Beudant (1787–1850).