The ruby gemstone is famous as one of the most valued gemstones in the world. Weight for weight, flawless rubies can be even more expensive than diamonds, and they belong in the Big Four (diamond, sapphire, ruby, emerald) precious gemstone group. Rubies are a type of corundum mineral (Al2O3) which is extremely hard; scoring 9 on the Mohs scale, it is just a step below the diamond. The color of ruby ranges from pink to vermillion-red; basically any shade of red there is. There are some spectacular rubies that display dichroism (double types of hue) and asterism (a 6 pointed
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