Gems Rough International Gems Rough International Friday, August 13, 2010 Epidote Minerals and Faceted Stones Epidote is a calcium aluminium iron sorosilicate mineral , Ca 2 Al 2 (Fe 3+ ;Al)(SiO 4 )(Si 2 O 7 )O(OH), crystallizing in the monoclinic system. Well-developed crystals are of frequent occurrence: