Characteristics of trapiche blue sapphires from southern Vietnam

Abstract

Trapiche patterns are common in emeralds but less common in corundum, and are typically restricted to ruby. Trapiche sapphire is comparatively rare. Blue sapphires of the trapiche type from southern Vietnam reveal a distinct core and fixed six-rayed star, similar in appearance to the patterns found in some rubies from Mong Hsu, Myanmar. The trapiche consists of dark brown to brown core, six blue sectors separated by six brown to brownish yellow arms of the star. Some samples also show a distinct colour zoning. A massive concentration of needle-like inclusions is seen in the arms under the microscope. These are oriented perpendicular to the hexagonal crystal faces. A number of inclusions are also observed in the core area. Gemmological, microscopic, spectroscopic, and chemical properties are presented to describe the characteristics of the blue sapphires from southern Vietnam.