Tacharanite
| Tachanarite | |
|---|---|
Globular, white tacharanite (diameter 2.5 mm) from Palagonia, Italy | |
| General | |
| Category | Minerals |
| Formula | Ca12Al2Si18O33(OH)36 |
| IMA symbol | Tch |
| Strunz classification | 9.HA.75 |
| Dana classification | 72.3.2.6 |
| Crystal system | Monoclinic |
| Space group | A-centered |
| Unit cell | a = 17.07 Å, b = 3.65 Å, c = 27.9 Å β = 114.1° Z = 1 V = 1,586.80 Å3 |
| Identification | |
| Formula mass | 2,180.68 g/mol |
| Color | Milky white |
| Crystal habit | Cryptocrystalline |
| Cleavage | Perfect {001} |
| Fracture | Conchoidal |
| Tenacity | Tough |
| Mohs scale hardness | 5 |
| Luster | Vitreous, earthy, dull |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.33 – 2.36 |
| Density | 2.33 – 2.36 g/cm3 Calculated: 2.28 g/cm3 |
| Optical properties | Biaxial |
| Refractive index | nα = 1.518 – 1.525 nγ = 1.530 – 1.537 |
| Birefringence | 0.0120 |
| Dispersion | Relatively strong |
| Fusibility | Decompose |
| Common impurities | Fe, Mg, Na, K |
| Other characteristics | Non radioactive |
| References | |
Tacharanite is a calcium aluminium silicate hydrate (C-A-S-H) mineral of general chemical formula Ca12Al2Si18O33(OH)36 with some resemblance to the calcium silicate hydrate (C-S-H) mineral tobermorite. It is often found in mineral assemblage with zeolites and other hydrated calcium silicates.
C-S-H and C-A-S-H mineral phases are important hydration products of cements but can also be found, although much less frequently, in natural conditions in particular geological environments. The natural specimens are rare and of small size (often available only in limited quantity) but often well crystallised while the hydrated cement phases are disordered and cryptocrystalline or amorphous with a poorly defined stoichiometry denoted by the use of dashes in the abbreviations C-S-H and C-A-S-H.