Ruby is a precious gemstone and a variety of the mineral corundum, celebrated for its intense red color—often called “pigeon blood red” in the finest specimens—caused by trace amounts of chromium. It has a hardness of 9 on the Mohs scale, making it one of the toughest gemstones after diamond. Valued for its vivid hue, rarity, and durability, ruby is the traditional birthstone for July and has symbolized passion and protection throughout history.