A gem or gemstone is known as a precious or semi-precious stone that is a part of some attractive mineral and used after cutting and polishing to make jewelry and other ornamentation. There are also some rocks and natural materials that are not minerals but still they are used to make jewelry and other ornamentation. These kinds of materials are also considered gemstones. A large number of gemstones are consisted of hard substances but some of them are soft minerals too.A gemologist has to test a wide range of materials as to confirm it as a gemstone. According to some estimates there are almost 270 varieties that have been identified.