Global InformationBarbertonite information
| Barbertonite | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | 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 | [1][2][3] |
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).[4] Mills et al. (2011) presented evidence that barbertonite is a polytype of stichtite and should be discredited as a mineral species.[5]
- ^ "Barbertonite Mg6Cr2(CO3)(OH)16·4H2O" (PDF). RRUFF.
- ^ Barbertonite: mindat.org
- ^ Barbertonite: webmineral.com
- ^ Taylor, H. F. W. (1973). "Crystal structures of some double hydroxide minerals". Mineralogical Magazine. 39 (304): 377–389. doi:10.1180/minmag.1973.039.304.01. ISSN 0026-461X.
- ^ Mills, S. J.; Whitfield P. S.; Wilson S. A.; Woodhouse J. N.; Dipple G. M.; Raudsepp M.; Francis C. A. (2011). "The crystal structure of stichtite, re-examination of barbertonite, and the nature of polytypism in MgCr hydrotalcites". American Mineralogist. 96 (1): 179–187. Bibcode:2011AmMin..96..179M. doi:10.2138/am.2011.3531. S2CID 55810652.