| Ludwigite | |
| Category: | Borate mineral |
| Formula: | Mg2Fe3+BO5 |
| Imasymbol: | Ldw[1] |
| Molweight: | 195.26 g/mol |
| Strunz: | 6.AB.30 |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pbam |
| Unit Cell: | a = 9.26, b = 12.26 c = 3.05 [Å]; Z = 4 |
| Color: | Pitch-black, olive-black |
| Habit: | Massive – fibrous commonly in fanlike to felted aggregates |
| Cleavage: | [001] Perfect |
| Fracture: | Brittle – Conchoidal – Very brittle fracture producing small, conchoidal fragments. |
| Mohs: | 5.5 |
| Luster: | Silky to submetallic |
| Refractive: | nα = 1.830 – 1.850 nβ = 1.830 – 1.850 nγ = 1.940 – 2.020 |
| Opticalprop: | Biaxial (+) |
| Birefringence: | δ = 0.110 – 0.170 |
| Pleochroism: | X = Y = dark green; Z = dark reddish brown |
| 2V: | Measured: 20° to 45° |
| Streak: | Greenish black |
| Gravity: | 3.6 – 3.8 |
| Solubility: | Slowly soluble in acid |
| Diaphaneity: | Opaque, translucent in thin fragments |
| Alteration: | limonite |
| References: | [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 forms a solid solution series with the iron(II)-iron(III) borate mineral vonsenite.
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.[3]