Gemological-Mineralogical Characteristic of Spinels from Sri Lanka

Detailed mineralogical and gemological records were conducted on 340 unheated spinels from the Horana, Eheliyagoda, Ratnapura, and Okkampatiya mining areas in Sri Lanka. The color of Sri Lankan spinel varies greatly: in addition to the mainstream pink to purple pink, green and blue can also be seen. Compared with spinel from other regions such as Myanmar, Vietnam, and Tanzania, Sri Lanka's spinel has more abundant inclusions: several mining areas generally have inclusions such as dolomite, apatite, zircon, and chondrodite. Minerals such as graphite and forsterite are also found in spinel produced in the Horana region; graphite and rutile have been found in spinel produced in the Okkamptiya region. Partially healed fissures are most common in spinel in the Okkampatiya mining area; Unlike Vietnamese spinel, dislocations and growth structures are almost absent in Sri Lankan spinel. The LA-ICP-MS analysis results showed that there were no significant differences among the mining areas. LA-ICP-MS analysis of 5 Sri Lankan cobalt blue spinels showed a variation of 11 to 120 ppm in this chromogenic element. The UV visible absorption spectrum results show that Sri Lankan spinel has a combination spectra with variable ratios of the spectral components Cr³⁺, V³⁺ and Fe²⁺ from pink to red, orange, purple to purple, and blue-green. The results of infrared spectroscopy and laser Raman spectroscopy analysis showed that all samples showed no indications for heat treatment.