Adularescence

Adularescence is an optical effect in which a soft, often bluish or white glow seems to float across a gemstone as the stone or viewing angle changes. It is particularly associated with moonstone. The effect originates within the material rather than in a painted surface coating.

In conventional moonstone, light scatters within a structure of thin alternating layers of the feldspar minerals orthoclase and albite. Other feldspars can display related effects. The trade name rainbow moonstone is used for pale labradorite, illustrating why a commercial gem name and a mineral identification are not necessarily equivalent.

When describing a jewel, examine the stone under directional light and note the glow's colour, location and movement. Photographs from several angles are more informative than a single bright reflection. One blue flash in a photograph cannot establish mineral identity, natural origin or geographical source. Describe an unidentified stone cautiously until closer examination provides the necessary evidence.

Sources: GIA: Moonstone Description; GIA: Moonstone Jewelry, 2019.