Legrandite

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Legrandite
LegranditeMexique.jpg
Yellow radiating prismatic crystals on limonite, from Ojuela Mine, Mun. de Mapimí, Durango, Mexico. Large crystal is 1.4 cm. long.
General
Category Arsenate minerals
Formula
(repeating unit)
Zn2(AsO4)(OH)·(H2O)
Strunz classification 08.DC.10
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: P 21/c
Unit cell a = 12.805(2) Å, b = 7.933(1) Å, 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
Crystal system Monoclinic
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, kottigite, 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, USA.[1]

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

References[edit]

Radiating cluster of legrandite crystals to nearly 4 cm, on limonite matrix. Ojuela mine, Mun. de Mapimí, Durango. Size: 6 x 3.8 x 3 cm.