Barbertonite
| Barbertonite | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula | Mg6(Cr,Al)2(OH)16CO3·4H2O |
| Strunz classification | 5.DA.45 |
| Crystal system | Hexagonal |
| Crystal class | Dihexagonal dipyramidal (6/mmm) H-M symbol: (6/m 2/m 2/m) |
| Space group | P63/mmc |
| Unit cell | a = 6.17 Å, c = 15.52 Å; Z = 1 |
| Identification | |
| Color | Intense violet to rose-pink |
| Crystal habit | flattened plates, in fibrous matted masses, and as cross-fiber veinlets |
| Cleavage | Perfect on {0001} |
| Tenacity | Flexible but not elastic |
| Mohs scale hardness | 1+1⁄2–2 |
| Luster | Waxy, pearly |
| Streak | Very pale violet to white |
| Diaphaneity | Transparent |
| Specific gravity | 2.05–2.15 |
| Optical properties | Uniaxial (−) may appear biaxial due to strain |
| Refractive index | nω = 1.557 nε = 1.529 |
| Birefringence | δ = 0.028 |
| Pleochroism | Weak, O = dark rose-pink to violet; E = pale rose-pink to violet |
| References | |
Barbertonite is a magnesium chromium carbonate mineral with formula of Mg6Cr2(OH)16CO3·4H2O. It is polymorphous with the mineral stichtite and, along with stichtite, is an alteration product of chromite in serpentinite. Barbertonite has a close association with stichtite, chromite, and antigorite (Taylor, 1973). Mills et al. (2011) presented evidence that barbertonite is a polytype of stichtite and should be discredited as a mineral species.