Gemstones are minerals that are cut and polished into various shapes and sizes. Some of the most precious gemstones are emeralds, rubies, diamonds, black pearls, and topaz. Gemstones are formed either near the bottom of volcanoes from cooling magma, or in underground caves rich in mineral water. Gems are evaluated based on their color, clarity, cut, and carat weight, and can fall into price categories like traditional gems, new classics, connoisseur gems, or affordable gems depending on these qualities.