Rubies, known as the “king of precious stones,” captivate with their intense red hue and timeless beauty, carrying a legacy of passion, power, and prosperity through the ages. As one of the most coveted gemstones in the world, rubies continue to enchant and fascinate both gem enthusiasts and collectors alike. Discover the allure of rubies showcased in the gemstones and jewelry by American Gem Society (AGS) members. What is a ruby? Ruby gemstones are a variety of the mineral corundum. More specifically, they are the red variety, which is colored by chromium. Other colors of corundum are classified as sapphire.