Legrandite
(repeating unit)Zn2(AsO4)(OH)·(H2O) IMA symbol Leg[1] 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 Identification 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 [2][3][4] 
(same H-M symbol)
c = 10.215(2) [Å]; β = 104.23°; Z = 8
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.[2][3] It has been reported from Tsumeb, Namibia; the Ojuela mine in Durango, Mexico and at Sterling Hill, New Jersey, US.[2]
It was first described in 1934 for an occurrence in the Flor de Peña Mine, Nuevo León, Mexico and named after Louis C.A. Legrand, a Belgian mining engineer.[3]
References
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