Ruby

Ruby is actually a red sapphire which is a species of corundum. Sapphire comes in every color and shade you can think of except for red, then we call it ruby. Red is the most rare color in gemology in general so during the time Rubies were first being discovered in south and south east Asia they were highly prized, so today we still call them by a different name. Rubies get their pinkish red color primarily from the presents of chromium on the stone and the more chromium in the stone the more it will fluoresce under UV light. Since rubies are corundum also known as sapphire, they are the 3rd hardest stone just under Moissanite and Diamond

Hardness: 9
Composition: Al₂O₃