ekanite, gems

Gübelin gives a detailed gemological account of ekanite, a newly recognized metamict gem mineral from Ceylon, named for F. L. D. Ekanayake, who first recognized its unusual character. The material occurs in the gem gravels near Ellawala, northeast of Ratnapura, and is typically greenish-brown to yellowish-green, transparent to translucent, and sometimes displays chatoyancy or asterism caused by oriented clouds of minute inclusions. Gübelin describes its gemological properties, including its singly refractive character, refractive index of about 1.595, specific gravity of about 3.28, and weak absorption bands, together with microscopic features and inclusions. Chemical investigation showed calcium, thorium, silicon, aluminium, and lead, while measurements demonstrated significant radioactivity associated particularly with thorium. The destruction of the original crystal lattice through radioactive decay accounts for its metamict condition. Gübelin also discusses its probable original crystalline state, chemical composition, and age as estimated by thorium-lead dating, establishing ekanite as an unusual new addition to the gem minerals of Ceylon.