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Anorthite skarn with dispersed chromium-hydrogrossular from Muslim Bagh area, Pakistan
Journal
The Australian Gemmologist
Volume
26
Number
11-12
Pages / Article-Number
286-290
Keywords
anorthite skarn, Cr-hydrogrossular, Muslim Bagh, Pakistan
Abstract
A white to light green opaque ornamental rock with green spots, collected near Muslim Bagh, Balochistan, Pakistan was submitted for identification. Thin sections for petrographic investigation were produced and the mineral components identified optically and by Raman spectrometry. Idiomorphic bright green Cr-hydrogrossular crystals are irregularly dispersed throughout the white ground mass of basic plagioclase. Further components comprise minor diopside with clinozoisite, zoisite and zeolites on fractures. Besides Sannan Skarn, this new ornamental stone is far away from belong to the jade group as it is composed of numerous minerals that do not belong to the pyroxene group. It can therefore not be sold as "a kind of jade". The rock has a specific gravity of 2.73 and a refractive index of approximately 1.57 (spot reading done on cabochons, using the same method as gemmologists use on moonstone or jadeite). This material is similar to a rock from Zambales, Luzon, Philippines that was identified as anorthosite, the main constituent mineral is anorthite, an end member of the feldspar group, with idiomorphic small uvarovite crystals.
