gems, spinel, inclusions, Sri Lanka

A comprehensive mineralogical and gemological study was conducted on 340 unheated spinels from Sri Lanka, specifically from the mining areas of Horana, Eheliyagoda, Ratnapura, and Okkampatiya. Sri Lankan spinels exhibit a wide range of colors, including the commonly seen pink to purplish pink, as well as green and blue hues. Compared to spinels from other regions like Myanmar, Vietnam, and Tanzania, Sri Lankan spinels are notably richer in inclusions. Common inclusions across the studied areas include dolomite, apatite, zircon, and chondrodite. Additionally, spinels from Horana contain graphite and forsterite, while those from Okkampitiya include graphite and rutile. Partially healed fissures are prevalent in Okkampitiya spinels, but unlike Vietnamese spinels, dislocations and growth structures are generally absent. LA-ICP-MS analyses revealed no significant geochemical differences among the mining regions, though cobalt-blue spinels showed Co concentrations ranging from 11 to 120 ppm. UV-visible absorption spectra demonstrated variable contributions of Cr³⁺, V³⁺, and Fe²⁺, which account for the spinels’ color variations from pink, red, and orange to purple and blue-green. Infrared and Raman spectroscopy confirmed that none of the analyzed samples showed evidence of heat treatment.