Kyanite is a mineral of metamorphic, alumina-rich rocks, the structure of which may include a small amount of ferric iron. The mineral contains impurities of alkali oxides, sometimes oxides of Ca, Mg, 13 and Cr. In the island structure of kyanite, oxygen atoms form a weakly distorted cubic close packing. The SiO4 tetrahedra are bonded to the and Al atoms, while the additional oxygen atoms are bonded only to the Al atoms.
The mineral of the sillimanite group (kyalite) belongs to the effective types of refractory and ceramic raw materials. Kyanite as an end product is used in the following areas of refractory and ceramic production: in precision casting as an additive in some fused cast refractories and monolithic materials to control expansion, as a crack filler due to expansion properties, in accessories for firing and drying furnaces (cast load-bearing elements , furnace walls, etc.), in the production of steel airfoil components, as a reduction compensator in refractory ceramic bricks, as a raw material for the production of natural and synthetic mullite.
Kyanite has a strongly pronounced hardness anisotropy. Does not dissolve in acids. Not radioactive.
Kyanite forms elongated, flattened, foliated, often curved, prismatic to tabular crystals; dense fibrous and radially radiant to needle-like aggregates; granular and solid masses. Sometimes kyanite forms twins.
Kyanite has the following characteristics:
1. chemical corrosion resistance
2. high thermal impact mechanical strength
3. irreversible thermal expansion