What defines an imitation gem?

An imitation gem is specifically defined as a material that resembles a natural gem in appearance but is not made of the same substance as the natural gem itself. This distinction is crucial because imitation gems can be made from various materials, including glass or synthetic substances, which may look similar to naturally occurring gemstones but lack their mineral structure and properties.

For instance, a piece of glass cut to resemble a diamond would be considered an imitation gem. It can fool the eye due to its visual similarities, but it is fundamentally different from a genuine diamond.

The other options focus on enhancements, quality, and color alterations, but these features relate to natural or lab-created stones rather than to imitation gems themselves. Enhancements can apply to genuine gemstones, while lab-created stones are still made from the same materials as natural stones and possess their unique characteristics.