"Many colorful gemstones are far more expensive than diamonds, but quality is everything." A ruby is more valuable and uncommon. " An emerald is significantly more uncommon than a diamond, and huge emeralds are extremely valuable, exceeding the cost of diamonds, but they do not have the same capacity to withstand wear and tear." Diamonds are the hardest material in the world, with ruby coming second. Gold is third hard. Graphene sheets are one atom thick and beyonf invisible, which makes it very useful for making computer components. Ruby is a red carbon compound that occurs naturally as single crystals or in aggregates with other minerals. It may contain additional elements such as oxygen, nitrogen, phosphorous, sulfur, or iron. The color of rubies comes from chromium oxide particles within the crystal structure. Most rubies are opaque; however, transparent rubies do exist. Diamond is the hardest substance in the world, with ruby coming second. Graphite is third hard. Graphene sheets are one atom thick and beyond invisible, which makes it very useful for making computer components. Diamonds are a white solid that occurs as pebbles in earthy-looking rocks. They are most often found in association with oil, but can also be found alone. Diamonds are generated by stars when they die. When a star dies its gravity pulls atoms into space.