Moonstone Sri Lanka: Gemstone Information

Moonstone – Sri Lanka
Sri Lanka is an important source of moonstones which occur in feldsparrich dykes in the Central and Southern Provinces and also in abundance in the gems gravels of the latter. It has been reported that the principal area is the Dumbara district of the Central Province where it occurs as pebbles and irregular masses in the gem gravels and clay deposits, and is also obtained by quarrying an adularia leptite. In Sri Lanka colours range from misty white to soft grey, pale orange, with a silver-white or blue sheen. Stones with a fine blue sheen are now
rare. Meetiyagoda and Tissamaharama are notable localities. Smoky* moonstone, from a locality near Imbulpe, east of Ratnapura, is the name given to moonstones with grey body colour which is attributed to
Fe2+ –Fe3+ intervalency charge transfer. The dark body colour is said to enhance the blue sheen. Metiyagoda in southern Sri Lanka was an important twentieth-century locality producing fine material. The pegmatite is potassium-dominant (approx K/Na ratio 2:1); however, the correlation of colour and composition revealed that white moonstone is K-rich whilst the more desirable blue is sodium-dominant i.e. more albite than orthoclase. Similar moonstone deposits have been reported from the areas around Balangoda and Kundasale.
Most Sri Lankan moonstones have SG = 2.562.58 (generally nearer 2.56); RI usually 1.520–1.525; DR 0.005 indicative of K-feldspar.