More than 130 different types of minerals are used for gemstones. The most popular gemstones are diamonds, rubies, emeralds and sapphires. Other gemstones are classified as precious or semi-precious.
When gemstones are found in their natural state, they are quite ordinary looking. A good polish is required to bring out the shine, brilliance or sparkle. Amethyst at one time was considered a precious gemstone. However, that changed when large reserves were found in Brazil, reducing its value. Two gemstones much rarer than diamonds, the alexandrite and tanzanite, can change color, depending on lighting conditions and the orientation at which the gemstones are viewed.