Final answer:
Chatoyancy and asterism are optical effects in gemstones known as the 'cat's eye' and 'star', respectively. The correct answer is 'b. cat's eye and star'. Chatoyancy shows a sharp reflective line, while asterism displays a star pattern.
Step-by-step explanation:
Chatoyancy and asterism are optical phenomena associated with certain gemstones. Chatoyancy, often referred to as the 'cat's eye' effect, is an optical reflectance effect seen in some gemstones, such as chrysoberyl, where a sharp line of light that shifts with the angle of the light source is visible across the surface of the stone. Asterism, on the other hand, is the phenomenon where a star-shaped pattern appears within a stone, typically visible under direct light, as seen in stones like star sapphires or star rubies.
The correct answer to the question would be 'b. cat's eye and star', as chatoyancy is where the term 'cat's eye' originates due to the similarity in appearance to the slit eye of a cat, and asterism is where the gemstone shows a star pattern, usually with four, six, or sometimes twelve rays.