Try to scratch the surface.

Only a diamond can scratch a ruby. Composite rubies are not as durable as real rubies. There is a chance that the ruby is not a complete "fake," and just a machine-made stone.

Can you break a real ruby?

Corundum (ruby and sapphire) is relatively hard—9 on the Mohs scale. It has excellent toughness and no cleavage, which is a tendency to break when struck. This makes it a great choice for rings and other mountings subject to daily wear. Ruby ranks 9 on the Mohs hardness scale, so it's an effective jewelry stone.

How can you tell if a ruby is real or fake?

Since many artificial rubies use glass or glass combinations, use the glass-to-glass comparison test to check authenticity. All you need is a piece of glass that's a similar color and hue. If the two have the same color, you have a fake ruby. Rubies will never be the same color as regular glass.