Adularescence

Adularescence (/ˌædʒələˈrɛsəns/ AJ-ə-lə-RES-əns) is an optical phenomenon that is produced in gemstones like moonstone.

The effect of adularescence, also commonly referred to as schiller or shiller, is best described as a milky, bluish luster or glow originating from below the surface of the gemstone.

[1] Though white schiller is the most common, in rarer specimens, orange or blue lusters are produced.

[3][4][5] Adularescence appears in numerous other gemstones, notably common opal, rose quartz and agate.

The schiller is scattered by inclusions and appears hazy; non-hazy specimens are specially referred to as "milky".

Adularescence in a moonstone cabochon , Minas Gerais , Brazil. The specimen's diameter is 23 mm (0.91 in).