Aluminosilicate
the group of aluminosilicates
Of general formula Al2SiO5 it includes/understands three polymorphic:
- *la orthorhombic Sillimanite of d=3,25:
- *l' orthorhombic Andalusite of d=3,15:
- *le Disthene or kyanite of d=3,60 more compact and triclinic.
- *l' orthorhombic Andalusite of d=3,15:
With low Pressure and high Temperature, starting from sillimanite or andalusite one obtains mullite more quartz. Mullite is the most important phase in the diagram of phase SiO2 - Al2O3. The transformation is irreversible, because mullite is stable at all the temperatures: it is thus very widespread in the artificial products (“refractory sillimanitic”). Nevertheless, it is rare in the natural rocks, which were formed under high pressures. On the other hand, the polymorphic ones of Al2SiO5 are formed with higher pressures and are thus common in kind.
The the most important layer of mullite is that of the island of Mull, in Scotland, where it was formed under exceptional conditions of high temperatures and relatively low pressures.
See too
| Random links: | Charnas | Andre Verchuren | Gaston Monmousseau | Bit (island) | Curtis Paper Millet | Acte_patient_d'autodétermination |