how to identify a real crystal whether it is synthetic or glass?

Answer 1

Test its specific gravity and do a scratch test. Refractive index test can help too.

Answer 2

It depends on the type of crystal.

Glass can usually be distinguished by it's hardness and index of refraction. Most glass usually has a hardness of around 5.5 mohs

The presence of bubbles and conchoidal fracture also suggests glass.

As for gemstones, synthetic gemstones are often made of the same stuff natural gemstones are, but an experienced jeweler can often tell them apart.

Answer 3

A 'synthetic' crystal, if it's a true crystal, would be
indistinguishable from a natural one except by
detailed chemical analysis.
Glass will exhibit a 'chonchoidal` fracture where
a crystal will have fracture planes.
Glass will typically be softer than most crystals,
but not all.

Answer 4

I think if you flick it with your finger and it goes "piiing" it's real and if it just goes "clink" it's fake. You can also wet your finger and rub it around the rim and if it "sings" it's real.