A ruby is a very hard stone, a 9 on the Mohs scale. It is second in durability only to the diamond, meaning that only a diamond (or an object with the hardness of a diamond) can scratch it. In comparison, glass is a mere 5.5. ... A real ruby cannot be scratched so easily.

How can I tell if a ruby is glass filled?

How can I tell if a ruby is glass filled? The most notorious visual characteristic of a composite ruby is the internal gas bubbles. These can be single spheres or clouds of bubbles, flattened or rounded, and they are present in virtually all fissure filled rubies.

How can you tell a real ruby from a fake?

Real rubies glow with a deep, vivid, almost "stoplight" red. Fake gems are often dull: they are "light, but not bright." If the gem is more of a dark red, then it may be garnet instead of a ruby. If it is a real ruby, however, know that darker stones are usually worth more than lighter stones.