Feature
Gems & Gemology, Spring 2007, Volume 43, No. 1
Trapiche Tourmaline from Zambia
Thomas Hainschwang, Franck Notari, and Björn Anckar
Well-formed crystals of green tourmaline from northwestern Zambia show a growth pattern reminiscent of trapiche emerald/ruby when sliced perpendicular to the c-axis. In fact, such slices were originally encountered in parcels sold as emerald in Zambia. The trapiche appearance most likely originates from skeletal growth, with the pattern formed by a black carbonaceous substance (mostly graphite) that partially filled growth tubes concentrated in three areas: (1) along the three edges of the trigonal pyramids r {101–1} or r’ {011–1 – }, (2) at the interface between the trigonal pyramids and the prism a {112–0}, and (3) between individual growth sectors of the prism a. Spectroscopic and chemical analyses indicate that the tourmaline is uvite that is colored green by a vanadium-related mechanism. To the authors’ knowledge, this is the first occurrence of trapiche tourmaline.
