Ruby is one of the four precious gemstones. The others are emerald, sapphire, and diamond.
Ruby comes from the Latin "rubens" meaning red.
Rubies are made of corundum. Corundum comes in many other colors, but those colors are classified as sapphires.
Ruby gets its red coloring from trace amounts of chromium.
Ruby measures 9 on the Mohs Scale of Hardness, second only to diamond and matched with sapphire, which means ruby an extremely hard and durable gemstone.
The most desirable shade of ruby is a deep red with a hint of blue which is referred to as "pigeon's blood."
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