Ludwigite

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Ludwigite
Ludwigite-242641.jpg
Radial aggregates of lustrous, black, metallic, acicular ludwigite crystals to 0.5 cm, from Alta Stock, Salt Lake County, Utah, USA.
General
Category Borate mineral
Formula
(repeating unit)
Mg2Fe3+BO5
Strunz classification 06.AB.30
Crystal symmetry Orthorhombic 2/m 2/m 2/m Space Group: Pbam
Unit cell a = 9.26 Å, b = 12.26 Å, c = 3.05 Å; Z = 4
Identification
Formula mass 195.26
Color Pitch-black, olive-black
Crystal habit Massive - fibrous commonly in fanlike to felted aggregates
Crystal system Orthorhombic
Cleavage [001] Perfect
Fracture Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments.
Mohs scale hardness 5.5
Luster Silky to submetallic
Streak greenish black
Diaphaneity Opaque, translucent in thin fragments
Specific gravity 3.6 - 3.8
Optical properties Biaxial (+)
Refractive index nα = 1.830 - 1.850 nβ = 1.830 - 1.850 nγ = 1.940 - 2.020
Birefringence δ = 0.110 - 0.170
Pleochroism X = Y = dark green; Z = dark reddish brown
2V angle Measured: 20° to 45°
Solubility Slowly soluble in acid
Alters to limonite
References [1][2]

Ludwigite is a magnesium-iron borate mineral: Mg2FeBO5.

Ludwigite typically occurs in magnesian iron skarn and other high temperature contact metamorphic deposits. It occurs in association with magnetite, forsterite, clinohumite and the borates vonsenite and szaibelyite.[2] It forma a solid solution series with the iron(II)-iron(III) borate mineral vonsenite.[1]

It was first described in 1874 for an occurrence in Ocna de Fier, Banat Mountains, Caras-Severin, Romania and named for Ernst Ludwig (1842–1915), an Austrian chemist at the University of Vienna.[1]

References[edit]


Ludwigite needles and sprays as inclusions in a peridot crystal from Sapat Gali, Kohistan District, Pakistan. Size 2.8 x 2 x 1.1 cm.