Moonstone, considered to be the most valuable variety of feldspar, is the opalescent variety of orthoclase (an opaque to transparent potassium feldspar). Its schiller or adularescence is caused by the intergrowth of two different types of feldspar, with different refractive indexes.
Like labradorite, it has an opalescent quality, caused by the reflection of light from the internal structure. Moonstone is usually whitish-blue, but can be colorless, yellow, orange, gray, or even reddish.
Like many gems found in Sri Lanka (formerly Ceylon) and Myanmar (formerly Burma), moonstone most often occurs as pebbles and irregular masses in gem-gravels and clay-deposits.
Mining moonstone is nearly always a manual process but there are several different ways in which stones can be collected:
In one method, miners dig deep narrow holes in the earth, lowering themselves by rope to the bottom. Filling their wicker baskets with loose dirt and gravel, they hoist the baskets back up to the surface where the gravels can be washed by hand to expose gem quality moonstones that can then be picked out of the gravel.
Another method, often referred to as "alluvial," is used in streams and rivers. In this process, natives use loosely-woven pans made from bamboo to 'wash' the river gravels, sands, and soils, allowing them to 'sift' the the water.
Occurring in colors ranging from misty whites to soft grays to pale oranges, Sri Lanka has produced the most desirable and enchanting specimens of moonstone for hundreds, if not thousands, of years.
Described as "situated somewhat in the hinterland," Sri Lanka's tiny hamlet of Domanwila, in the village of Mitiyagoda (also known as Meetiyagoda), dominates the world's moonstone market.
The village is especially known for its "blue flash" moonstone, translucent white with brilliant flashes of a metallic shimmer-y bright blue. Providing steady employment (a rarity in Sri Lanka), the moonstone industry supports the village.
The orthoclase layer under the village is only about 20-30 feet down making manual, low cost access possible. This is particularly beneficial in a culture dependent on the gem trade where men often have to leave home for many months at a time to mine in remote areas of the country, living under the most primitive conditions.
However, the advantage also comes at a cost: abandoned mines have turned into stagnant polluted water holes that breed ever more mosquitoes, making malaria and other mosquito-borne diseases a huge problem.
Recommended review time for sightseeing: 1 h