A new deposit of andradite garnet of the demantoid and topazolite varieties has recently been discovered in Antetezambato, Ambanja area, Antsiranana province, North Madagascar.
The absence of titanium in the sedimentary rocks accounts for the crystallization of the demantoid and topazolite varieties rather than the more common titanium-rich melanite variety of andradite.
The two andradite varieties of principal interest are demantoid and topazolite.
Topazolite is another variety of andradite, characterized by a brownish orange color, sometimes with a greenish tint which grades into yellow-green demantoid (Gramaccioli, 1975; Rouse, 1986).
Before the discovery of the Madagascar occurrence, topazolite was only very rarely found as attractive, collectible crystal specimens; moreover, this garnet variety has generally been considered to be of no gem interest (Anderson, 1975) and information in the literature is rather scarce.
The classic occurrence in Val d' Ala (the Ala Valley) in Piedmont, Italy remains one of the most significant sources of topazolite crystal specimens; Ala Valley topazolite has been found in crystals occasionally exceeding 1 cm in diameter, but only the smallest crystals are of gemmy quality.
Concerning the yellow and yellow-brown color varieties of gem andradite, there is general agreement among gemological writers on the varietal name topazolite, regardless of the causes of the color.
Andradite [[Ca.sub.3][Fe.sub.2.sup.3+]([SiO.sub.4]).sub.3]] crystals of the demantoid and topazolite varieties are found at Antetezambato as detached crystals and crystal groups, but most commonly as matrix specimens in ail sizes from thumbnails to large cabinet specimens.
Some EDS microprobe spectra (requiring confirmation) indicate very minimal traces of titanium in one brownish crystal (topazolite), and titanium, vanadium and copper in one vivid green crystal with a bluish tint (demantoid).
Gem andradite crystals from Antetezambato can be divided into (1) the demantoid variety of yellow-green to army-green, grass-green, emerald-green, and bluish green color, often of low to moderate saturation, and (2) the topazolite variety of honey-yellow, amber-yellow, brownish yellow and brown color.