Kosgoda Sea Turtle Conservation Project
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.