Moonstone is a favorite gem here at Tapphire Creations, and when we found adjustable sterling silver ring bases (yes you read that right) we couldn't wait to set one with moonstone.  
 
This stone is a 10mm moonstone.  Please take care as moonstone is a softer stone and should only ever be cleaned with warm soapy water.  Do not use ultrasonic or steam to clean your moonstone.