Mineralogy of a scapolite-bearing rock from Rajasthan, Northwest Peninsular India

Sharma, Ram S. (1981) Mineralogy of a scapolite-bearing rock from Rajasthan, Northwest Peninsular India Lithos, 14 (2). pp. 165-172. ISSN 0024-4937

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Related URL: http://dx.doi.org/10.1016/0024-4937(81)90052-9


Electron-microprobe analyses of coexisting phases from a scapolite-garnet-epidote-calcite-plagioclase-hornblende-pyroxene (sphere-hematite-magnetite) rock of the Aravalli Group (Early Precambrian) at Karera, district Bhilwara, Rajasthan, reveal that chlorine is an important constituent of both scapolite (Me71.3 and hornblende, making the latter a dashkesanite variety. The amphibole also contains an unusually high K2O (3.7 wt.%), and is a chlor-potassium hastingsite. The epidote contains 41% pistacite and shows complete substitution of Al by Fe3+ in the Al-site and to some extent also in AIO and/or Al(OH) sites. The garnet is also rich in ferric iron and has a mol. composition Pyr23Alm8.5Gro13And54.5 Sp1.0. The pyroxene is dominantly a hedenbergite. The phase relations and textural as well as geological criteria exclude metasomatic processes and favour equilibrium recrystallization of the scapolite-bearing assemblage; the chlorine presumably derived from an evaporite component of the Aravalli metasediments. The geothermometry based on the fractionation of Na and Ca between scapolite (EqAn 43.3) and plagioclase (An85-90 yields metamorphic temperatures of around 700°C for the scapolite-bearing rock which are in agreement with those obtained by other mineral equilibria in the associated pelitic assemblages.

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