Sekaninaite
| Sekaninaite | |
|---|---|
Sekaninaite from Dolní Bory, Czech Republic | |
| General | |
| Category | Cyclosilicate |
| Formula | (Fe+2,Mg)2Al4Si5O18 |
| IMA symbol | Skn |
| Strunz classification | 9.CJ.10 |
| Dana classification | 61.02.01.02 Cordierite group |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Cccm |
| Unit cell | a = 17.18 Å, b = 9.82 Å c = 9.29 Å; Z = 4 |
| Identification | |
| Color | Blue to blue-violet |
| Crystal habit | As poorly developed crystals |
| Twinning | Commonly twinned on {110} and {310} |
| Cleavage | {100}, imperfect; parting on {001} |
| Mohs scale hardness | 7 – 7.5 |
| Luster | Vitreous |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.76 – 2.77 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.561 nβ = 1.572 nγ = 1.576 |
| Birefringence | δ = 0.015 |
| 2V angle | Measured: 66°, Calculated: 60° |
| References | |
Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a silicate mineral, the iron-rich analogue of cordierite.
It was first described in 1968 for an occurrence in Dolní Bory, Vysočina Region, Moravia, Czech Republic, and is now known also from Ireland, Japan, and Sweden. It was named after a Czech mineralogist, Josef Sekanina (1901–1986). In Brockley on Rathlin Island, Ireland sekaninaite occurs in bauxitic clay within the contact aureole of a diabase intrusive plug.