Ludwigite
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Ludwigite | |
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Radial aggregates of lustrous, black, metallic, acicular ludwigite crystals to 0.5 cm, from Alta Stock, Salt Lake County, Utah, USA.
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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
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