simulant

Simulating (something else); appearing to be (what it is not); replacing (in position or in aspect): with of: used especially in biology: as, a scutum simulant of a scutellum; cheliceres simulant of chelæ; stamens simulant of petals, or conversely.

One who or that which simulates something else.

Something that simulates something else such as, for example, a gemstone.