Imitation diamonds or fake diamonds are also known as faux diamonds. Or "simulant" as used by the industry insiders. It refers to materials, such as CZ, that look like another gem.
Cubic zirconia is a synthetic gemstone often used as an imitation for diamond due to its similar appearance and sparkle.
Ideally, you'd replace a diamond with another diamond. Or if you wanted the empty space to look like the diamond was still there, you could replace it with an imitation diamond. You can replace a diamond with almost any faceted stone.
Lure
rhinestone
Probably not, sorry. You may be able to find an imitation, though.
counterfeiting
So-called "copycat" offenses.
Onomatopiea.
Simulant.
The imitation of natural sounds or words that sound like the sound they are supposed to make is called onomatopoeia.
canonic imitation is canonic imitation
Point of imitation