How do you know if it is real garnet?

Answer 1

In general, gemologists identify gemstones by physical characteristics such as chemical composition, refractive index, specific gravity and hardness. In the case of ruby, a gemologist also has to distinguish between natural ruby -- ruby occurring in nature -- and synthetic ruby -- ruby produced in a laboratory through a process such as flame fusion. One of the signature characteristics of a synthetic ruby is curved growth lines formed as the crystal grows upwards in an environment with a high thermal gradient.

Answer 2

OK- a genuine ruby will have inclusions called "silk", no matter the quality. If a red stone is 100% clear through a loupe, it is man-made.