Trapiche Crystals of Emerald, Ruby, Sapphire & Tourmaline

摘要

A rare type of emerald contains dark inclusions that radiate outward like the spokes of a wagon wheel. Known as trapiche, after the Spanish word for a sugar cane crushing gear that it resembles, similar sectored inclusions have also been found in ruby, sapphire, the chiastolite variety of andalusite, and more recently in tourmaline. The trapiche growth phenomenon has been variously interpreted as caused by simultaneous precipitation of both host and inclusion (Nassau and Jackson, 1970), skeletal or dendritic growth (Sunagawa, 1995; Hainschwang et al., 2007 [in tourmaline]); or exsolution (Hainschwang et al., 2007 [in sapphire]). Although trapiche crystals of different minerals share a number of common features, they also differ in the composition and crystallographic orientations of the inclusions. These are briefly summarized below.