Sturmanite
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CategorySulfate minerals
FormulaCa6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25 H2O
IMA symbolStrm[1]
Strunz classification7.DG.15
| Sturmanite | |
|---|---|
 Distinctive sturmanite on matrix from the N'Chwaning Mines. Size: 5.4 x 4.2 x 1.7 cm. Ex.Charlie Key Stock | |
| General | |
| Category | Sulfate minerals |
| Formula | Ca6Fe3+2(SO4)2.5[B(OH)4](OH)12 · 25 H2O |
| IMA symbol | Strm[1] |
| Strunz classification | 7.DG.15 |
| Dana classification | 32.4.4.2 |
| Crystal system | Trigonal |
| Crystal class | 3m - Ditrigonal Pyramidal |
| Space group | P31c (no. 159) |
| Unit cell | a = 11.188(9) Å, c = 21.91(7) Å |
| Identification | |
| Color | Bright yellow to amber |
| Crystal habit | Hexagonal, pyramidal, prismatic |
| Cleavage | Perfect {1010} |
| Tenacity | Brittle |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous, greasy |
| Streak | Pale yellow, greenish yellow, brownish orange |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 1.847 (measured) 1.855 (calculated) |
| Optical properties | Uniaxial (+/-) |
| Birefringence | δ = 0.002 |
| Ultraviolet fluorescence | none |
Sturmanite is a rare sulfate mineral with the chemical formula Ca6Fe3+2(SO4)2.5(B(OH)4)(OH)12 · 25 H2O.[2][3][4] It crystallises in the tetragonal system and it has a Moh's hardness of 2.5. Sturmanite has a bright yellow to amber colour and falls in the ettringite group. It was named after Bozidar Darko Sturman (born 1937), Croatian-Canadian mineralogist and Curator Emeritus of Mineralogy, Royal Ontario Museum.[5]