What term describes a laboratory-created gem that matches the natural stone in chemistry and structure?

The term that accurately describes a laboratory-created gem that matches the natural stone in chemistry and structure is "synthetic." Synthetic gems are created using advanced techniques that replicate the conditions under which natural stones are formed, resulting in a product that has the same chemical composition and crystalline structure as the natural counterpart. This means that while the synthetic gem is produced in a lab, its physical and optical properties are virtually indistinguishable from those of the natural gem.

In contrast, imitation gems do not share the same chemical composition or structure as the natural stones they mimic; instead, they might look similar but are made from entirely different materials. Reconstructed gems usually involve taking fragments of natural stones and binding them together or enhancing them, which does not equate to creating a perfect chemical match. Natural stones, on the other hand, are those that are formed in nature without human intervention, distinguishing them from synthetic stones. Therefore, "synthetic" is the correct term for a laboratory-created gem that is identical to its natural counterpart in composition and structure.