It is a member of the aluminium-silicate group of minerals where three minerals like andalusite, sillimanite and Kyanite have been included. All these are characteristic metamorphic minerals having the chemical composition-Al303Si02 where Al203 constitutes about 62 93% of the mineral. But they differ only in their crystallographic characters and other physical properties.

Origin:

Kyanite is believed to have been derived from the argillaceous rocks metamorphosed under moderate temperature and high stress. It is a characteristic mineral of regional metamorphic rocks of medium grade and is absent from normal contact aureoles.

Mode of occurrence:

ADVERTISEMENTS:

It occurs as disseminated crystals in schists, quartzites and gneisses produced by regional metamorphism and also as surface deposits containing pebbles and boulders.

Distribution:

Important deposits of Kyanite occur in the Singhbhum district of Bihar, along a belt 80 miles in length, stretch­ing east along the western part of Seraikela, through part of northern Singhbhum and Kharsawan into Dhalbhum. The Lapsa-Buru Kyanite deposit, which is the largest Kyanite deposit in the world, is situated in this belt. Along this belt, kyanite occurs in the form of boulders and pebbles. The country rock is mica-schist. According to Dunn, kyanite rocks represent a smaller area in the entire belt which were even more basic than a normal clay and which was most probably a bauxite clay and no free quartz had been formed, when the process of metamorphism converted the clay into kyanite.

Kyanite deposits have also been found in Purulia district of West Bengal and in Ranchi district of Bihar.

ADVERTISEMENTS:

Kyanite of a semi-precious variety is known to occur in asso­ciation with calcite in the hills of Narnaul, Patiala and is used in the local market as a gem-stone, known as ‘brug’.

Uses:

Kyanite after being calcined and grained to powder is used as a refractory material, as well as in ceramic industries. Transparent kyanite is used as ‘gem-stone’.