gems, Ceylon, Sri Lanka, ekanite, metamict mineral

Anderson, Claringbull, Davis and Hill describe ekanite, a newly recognized metamict mineral from the gem pits of Eheliyagoda in the Ratnapura district of Ceylon. Known since 1953 as green transparent-to-translucent pebbles, some fashioned as cabochons showing a gemstone-quality smoky asterism, the material was recognized as unusual by F.L.D. Ekanayake, after whom the mineral was named. Chemical analysis indicates a thorium-rich calcium silicate containing uranium, lead and minor rare-earth elements, with the approximate formula (Th,U)(Ca,Fe,Pb)₂Si₈O₂₀. The mineral is metamict, with refractive index about 1.5969 and density 3.276. Heating between 650 and 1,000 °C causes recrystallization to an X-ray powder pattern resembling thorite or zircon; at higher temperatures it melts and, if subsequently recrystallized, produces an X-ray pattern analogous to huttonite. Microscopic examination shows occasional larger opaque inclusions but no identifiable inclusions responsible for the asterism.