A proposed new classification for gem-quality garnets.

Abstract

This is the 'cap-stone' article by these authors concerning garnet gemstones (M.A. 85M/3116). The proposed system - based on >500 chemical analyses - recognizes the following eight 'species': grossular, andradite, pyrope, pyrope-almandine, almandine, almandine-spessartine, spessartine and pyrope-spessartine. Each is plotted on a spessartine-pyrope-almandine ternary composition diagram, and the following properties are tabulated: refr. ind. ranges, colour hues, spectral absorption features, absorption spectra (hand spectroscope) and descriptions of varieties. Varieties are attributed to the 'species' as follows: grossular - tsavorite and hessonite; andradite - demantoid and topazolite; pyrope - chrome pyrope; pyrope-almandine - rhodolite; pyrope-spessartite - malaia and colour-change pyrope-spessartine.-R.V.D.