Sri Lanka- 'The Pearl of the Indian ocean', lies at the southern tip of India which is located at latitude of 6° – 10° N and longitude of 80° – 82° E. The major part of Sri Lanka is made up of Precambrian crystalline rocks in addition to a belt of sedimentary rocks along the north-west coast of the country. The Precambrian rocks covers approximately 90% of Sri Lanka, have been classified into three major lithological units, which are Highland / Southwestern Complex, Vijayan Complex and Wanni Complex.
Sri Lanka is popular throughout the world for the large quantity and exquisite variety of its precious stones. These gemstones occur mainly in alluvial gravels found in valley bottoms into which flow tributary hillside streams that carry gem minerals released by weathering form the bed rock sources located at hilltops or hillsides. Apart from the sedimentary formation which carry gemstones some rocks too have been shown to contain precious stones particularly varieties of Corundum. There are also gemstones associated with pegmatite that constituted an important source.
During early times Sri Lanka was once quite fittingly referred to as “Rathna-deepa” that con notes the meaning “The Island of Gemstones”. The name Rathna-deepa is found in many chronicles. A Merchants Guide “Periplus of the Erythrean Sea” presumed to have been made during the first century.
At present around 200 minerals have been classified as gemstones either due to their beauty, durability, rarity or a combination of some of these attribute which should be fulfilled make a mineral worthy of being classified as a precious stone. Among these gemstones, around 75 varieties have been mined or found in the island called Sri Lanka. Though exploitation of Sri Lanka gemstone deposits has been going on for many centuries, its only in recent times that effort has been made to make study of the industry itself, the locations of possible gemstone deposits and most significantly.