Sri Lanka is one of the top gem bearing countries in the world with the highest density of gems in the world and is a global sourcing destination for over 75 varieties of precious and semi-precious gemstones.

Over the past few million years, intense weather and rapid erosion have given rise to thick and extensive accumulations of sediments in the flood plains of rivers, in lakes, and in now-buried river channels in the Highland complex. It is within these weathering products that significant secondary-alluvial-gem deposits are collected. Except for a few alluvial occurrences in the Eastern Vijayan Complex, virtually all Sri Lankan gem deposits have been found within the Highland and to a lesser extent Southwest Groups. Today. large expanses of alluvial deposits have been extensively mined in the main Ratnapura and Elahera gem fields in Sri Lanka, where a majority of coloured gemstones are found.