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Legrandite, limonite 1100.1.2839.jpg
Category Arsenate minerals
(repeating unit)
Strunz classification 8.DC.10
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/c
Unit cell a = 12.805(2), b = 7.933(1)
c = 10.215(2) [Å]; β = 104.23°; Z = 8
Color Bright yellow, wax-yellow, colorless
Crystal habit Crystalline, prismatic, typically in sprays or sheaflike aggregates
Cleavage Imperfect, poor one {100}
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 4.5-5
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.98–4.01
Optical properties Biaxial (+)
Refractive index nα = 1.675 - 1.702 nβ = 1.690 - 1.709 nγ = 1.735 - 1.740
Birefringence δ = 0.060
Pleochroism X = Y = Colorless to yellow Z = Yellow
2V angle Measured: 50°
References [1][2][3]

Legrandite is a rare zinc arsenate mineral, Zn2(AsO4)(OH)·(H2O).

It is an uncommon secondary mineral in the oxidized zone of arsenic bearing zinc deposits and occurs rarely in granite pegmatite. Associated minerals include: adamite, paradamite, köttigite, scorodite, smithsonite, leiteite, renierite, pharmacosiderite, aurichalcite, siderite, goethite and pyrite.[1][2] It has been reported from Tsumeb, Namibia; the Ojuela mine in Durango, Mexico and at Sterling Hill, New Jersey, US.[1]

It was first described in 1934 for an occurrence in the Flor de Peña Mine, Nuevo León, Mexico and named after M. Legrand, a Belgian mining engineer .[2]