| Bannisterite | |
|---|---|
 | |
| General | |
| Category | Mineral |
| Formula (repeating unit) | (Ca,K,Na)(Mn2+,Fe2+)10(Si,Al)16O38(OH)8 · nH2O n ~ 5.5 |
| IMA symbol | Ban[1] |
| Strunz classification | 9.EG.75 |
| Dana classification | 74.1.1.4 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic H-M Symbol: 2/m |
| Space group | B2/b |
| Unit cell | 8,955.48 |
| Identification | |
| Color | Dark brown |
| Cleavage | Perfect on {001} |
| Fracture | Micaceous |
| Mohs scale hardness | 4 |
| Luster | Sub-vitreous, resinous, greasy |
| Streak | Creamy white |
| Diaphaneity | Translucent |
| Specific gravity | 2.83 - 2.84 |
| Density | 2.83 - 2.84 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.544 - 1.574 nβ = 1.586 - 1.611 nγ = 1.589 - 1.612 |
| Birefringence | 0.045 |
| Pleochroism | Visible |
| 2V angle | 18°- 28° |
| Dispersion | Weak to moderate r < v |
| Ultraviolet fluorescence | None |
| Common impurities | Zn, Na |
Bannisterite is a mineral named in honor of mineralogist and x-ray crystallographer Dr. Frederick Allen Bannister (1901-1970). It is a calcium-dominant member of the ganophyllite group, and was previously identified as ganophyllite in 1936, but otherwise it is structurally related to the stilpnomelane group. It was approved by the IMA in 1967.[2]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ "Bannisterite". www.mindat.org. Retrieved 2021-09-27.