What does the term "extinction" refer to in the context of colored stones?

The term "extinction" in the context of colored stones specifically refers to the dark areas that can appear in a faceted transparent colored gemstone. When light enters a faceted gem, it can be reflected and refracted in various ways. Certain angles of viewing, known as extinction angles, cause portions of the gem to appear dark or black because those areas do not reflect light effectively. This phenomenon occurs due to the internal structure and orientation of the facets and the way they interact with light. It is an important aspect in the study of gem appearance and is often discussed in relation to the quality of cutting, as well as the overall brilliance and visual appeal of the stone.

The other options do not accurately represent the term:

• Bright areas in a gem describe where light is being effectively reflected and is not related to extinction.

• The method of altering color does not pertain directly to the concept of extinction.

• The complete absence of color refers to colorlessness, which is different from the specific phenomenon of dark areas resulting from extinction.