Vesuvianite: Gemstones Information
Vesuvianite is the preferred mineralogical name to the gemmologists’ idocrase, Ca19(Al,MgFe)13OSi18O68(OH,F)10 which is found as short to long prismatic tetragonal transparent crystals in various colours of which green, yellow and brown are the most common. Crystals are morphologically complex and there are chemical affinities with grossular with which it can be intergrown. The hardness is 6–7 and the SG 3.32–3.47. The RI for the ordinary and extraordinary rays is 1.703–1.752 and 1.700–1.746, uniaxial positive though biaxial examples have been recorded. The birefringence is very small.The ornamental material californite is a mixture of vesuvianite and grossular and can be quite an effective simulant of green jadeite from which it can be distinguished by the presence of an absorption band at 461 nm while the jadeite 437 nm band is absent. Some brown specimens may display fine-line RE absorptions.Vesuvianite occurs in skarns formed during contact or regional metamorphism of limestones in serpentines and ultramafic rocks. Some brown gem-quality material comes from Italy and Switzerland. Bright green specimens from Asbestos, Quebec, Canada, may be intergrown with grossular and when coloured by Cr are a fine deep green; some pink specimens are coloured by Mn. Vesuvianite is also reported from Kenya. Classic European localities for brown, yellow and other colours of vesuvianite are in Italy and Switzerland. Californite is found in the Pulga area of California. An unusually fine oval dark green faceted stone of 3.68 ct was shown to MO’D in December 2004 by Marcus McCallum.