Bustamite
Bustamite is a calcium manganese inosilicate (chain silicate) and a member of the wollastonite group. Magnesium, zinc and iron are common impurities substituting for manganese. Bustamite is the high-temperature polymorph of CaMnSi2O6 and johannsenite is the low temperature polymorph. The inversion takes place at 830 °C (1,530 °F), but may be very slow.
Bustamite could be confused with light-colored rhodonite or pyroxmangite, but both these minerals are biaxial (+) whereas bustamite is biaxial (−).
| Bustamite | |
|---|---|
Bustamite (pink) with galena (grey) from Broken Hill, New South Wales, Australia. Specimen size 3.7 cm. | |
| General | |
| Category | Inosilicate |
| Formula (repeating unit) | CaMn2+Si2O6 |
| IMA symbol | Bst |
| Strunz classification | 9.DG.05 (10 ed) 8/F.18.40 (8 ed) |
| Dana classification | 65.2.1.2 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal 1 (same H-M symbol) |
| Space group | I1 |
| Identification | |
| Color | Light pink to brownish red Pink color fades on exposure to sunlight |
| Crystal habit | Usually tabular or equant to prismatic; commonly massive, often compact and fibrous |
| Twinning | Rare. Simple twins with (110) as the composition plane |
| Cleavage | {100} perfect; {110} and {110} good; {010} poor |
| Mohs scale hardness | 5.5 to 6.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Translucent to transparent |
| Specific gravity | 3.32 to 3.43 (observed) 3.40 (calculated) |
| Optical properties | Biaxial (−), 2V=34° to 60° |
| Refractive index | nα = 1.640 – 1.695, nβ = 1.651 – 1.708, nγ = 1.653 – 1.710 |
| Birefringence | δ = 0.013 – 0.015 Dispersion r < v weak to strong |
| Pleochroism | Weak, X and Z orange, Y rose |
| Solubility | Partly soluble in HCl. |
| Other characteristics | lattice: A B1 Specimens from the Franklin Mine are fluorescent red in longwave ultraviolet light. Not radioactive |
| References | |
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