Adularia 319 ct Diamond shape 16.6 x 10.1 mm India y91025
a variety of Ortochlase with formula K( AlSi3O8) commonly knows as moonstone.
Tha hardness is 6.
This material is often cut in cabochon shapes in order to see the adularescence or shiller effect,with blue ,green and yellow flashes.Cat’s eye moonstone is the most popular , Facet moonstones like this one in the picture are not so common to find. The gem comes from India and is eye clean, slighty adularescence.