The occurrence of andalusite and sillimanite
in these rocks can be associated to a superimposed low-P/high-T thermal event, although the presence of these polymorphs implies pressure below the [Al.
The protrusion of fibrolitic sillimanite
from biotite into quartz is alarming because it creates tiny microscopic fractures which can make the affected quartz grains extremely susceptible to ASR in the presence of alkali dissolved water.
Beach placer deposits of India essentially consist of ilmenite, rutile, garnet, zircon, monazite, sillimanite
Rock-forming minerals such as kyanite, vanadian phlogopite, fuchsite, quartz, sillimanite
, and tourmaline group species occur in the vein rock.
Its trend NW-SE is also indicated by the orientation of sillimanite
nodules in sillimanite
-biotite paragneisses and migmatites.
These metamorphic rocks are made of minerals such as micas, garnet, kyanite, sillimanite
Haematite, tourmaline, zircon, rutile, ilmenite, sillimanite
, geothite, and chlorite were also observed in Fe-Mn concretions.
So far, more than 120 kyanite mineral districts have been found, of which 23 have proven reserves of 75M mt grading 10-20% kyanite group minerals (kyanite, sillimanite
, and andalusite).
The muffle used in tube furnaces is usually dust-free and impervious; the sillimanite
(aluminum silicate) muffle former used in chamber furnaces is not.
It is the third-richest country in bauxite, the largest exporter of cut and polished diamonds, and a key exporter of fabricated sheet mica, non-coking coal, sillimanite
, granite, vermiculite, magnesite, steatite and bentonite.
Recoverable reserves of selected Indian resources (Mt unless otherwise stated) Fuel minerals Reserve Coal 192,000 Lignite 6,473 Metallic minerals Chromite 88 Iron ore (hematile) 9,602 (magnetite) 3,143 Manganese ore 176 Bauxite 2,525 Copper ore 416 Gold ore 18 Lead-zinc ore 186 Titanium 102 Tungsten 26 Vanadium 13 Molybdenum (t) 5,389 Non-metallic minerals Apatite 13 Asbestos 23 Barytes 70 China clay 986 Diamond ('000 ct) 1,084 Dolomite 4,967 Gypsum 239 Kyanite 3 Limestone 76,446 Magnesite 233 Mica (t) 109,000 Rock phosphate 147 Beach sand sillimanite
51 Soapstone/steatite 84 Wollastonite 4 Source: Indian Bureau of Mines