Indialite

indialite

Images

Formula: Mg2Al3(AlSi5)O18
Cyclosilicate (ring silicate), hexagonal high-temperature paramorph of cordierite
Crystal system: Hexagonal
Specific gravity: 2.512 measured for artificial material, 2.59 calculated
Hardness: 7 to 7½
Colour: Colourless in thin section
Common impurities: Fe,Mn,Na
Environments

Volcanic igneous environments
Metamorphic environments
Coal-seam fires

Localities

At Nickenicher Weinberg, Nickenich, Pellenz, Mayen-Koblenz, Rhineland-Palatinate, Germany, indialite has been found with osumilite (Mindat photo).
Indialite from Nickenicher Weinberg - Image

At the type locality, the Bokaro coalfield, Ramgarh District, Jharkhand, India, indialite is formed by fusion and recrystallisation of sedimentary rocks as a result of the burning of underlying coal seams. Associated minerals include enstatite, magnetite, labradorite, corundum and glass (HOM).

At Belvedere, Ercolano, Metropolitan City of Naples, Campania, Italy, indialite has been discovered in unusual pyrometamorphic ejecta. The indialite-bearing xenoliths are composed of several pale yellow fragments consisting of very fine-grained indialite with traces of cristobalite. On the surface of the fragments, colourless indialite and pale-blue, prismatic osumilite crystals form whitish crusts, with subordinate phlogopite and trace amounts of corundum. Gypsum and iron-oxides are ubiquitous.
Indialite-bearing rocks originated through a pyrometamorphic process at shallow depth and at maximum temperature close to ~1200°C (AM 89.1-6).

At Unazuki, Kurobe City, Toyama Prefecture, Japan, indialite occurs in cordierite veins in a polymetamorphosed pelitic rock. Associated minerals include cordierite, andalusite, sillimanite, biotite and quartz (HOM).

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