Ludwigite is a magnesium -iron borate mineral : Mg2 FeBO5 .
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Ludwigite Radial aggregates of lustrous, black, metallic,
acicular ludwigite crystals to 0.5 cm, from Alta Stock,
Salt Lake County , Utah, USA.
Category Borate mineral Formula Mg2 Fe3+ BO5 IMA symbol Ldw[ 1] Strunz classification 6.AB.30 Crystal system Orthorhombic Crystal class Dipyramidal (mmm) H-M symbol : (2/m 2/m 2/m) Space group Pbam Unit cell a = 9.26, b = 12.26 [Å]; Z = 4 Formula mass 195.26 g/mol Color Pitch-black, olive-black Crystal habit Massive – fibrous commonly in fanlike to felted aggregates Cleavage [001] Perfect Fracture Brittle – Conchoidal – Very brittle fracture producing small, conchoidal fragments. Mohs scale hardness5.5 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 [ 2] [ 3]
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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 .[ 3] solid solution series with the iron(II)-iron(III) borate mineral vonsenite.[ 2]
It was first described in 1874 for an occurrence in Ocna de Fier, Banat Mountains , Caraș-Severin County , Romania and named for Ernst Ludwig (1842–1915), an Austrian chemist at the University of Vienna .[ 2]
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.
