Coated Stone

Coated Stone
A gemstone covered by an artificially applied transparent material to enhance its color. Often used with Topaz.

Physical Properties of Gemstones
The Crystallography and Forms of Gemstones
Types of Gemstone Deposits
Sources of Gemstones
Doublets, Coated Stones And Foilback
Identification By Double Refraction & Pleochroism ...

Advertising suggests (righfully so or not) that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant.

See also: Crystal, Facet, Hue, Reflection, Refraction