Beudantite

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
Large brown crystals of Beudantite.
General
Category	Arsenate minerals
Formula (repeating unit)	PbFe3(OH)6SO4AsO4
Strunz classification	8.BL.10
Dana classification	43.4.1.1
Crystal system	Trigonal
Crystal class	Hexagonal scalenohedral (3m) H-M symbol: (3 2/m)
Space group	R3m
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
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]

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]