Also called a gem, precious or semi-precious stone, a gemstone is a highly-prized mineral that has formed crystals and has been cut and polished professionally for use in jewelry or other ornaments. The main qualities of a gemstone are durability (which is not necessarily hardness), beauty (but beauty isn’t enough), and rarity. Today there are roughly 200 varieties of natural gemstones, but only four of them are considered precious (diamonds, emeralds, rubies, and sapphires). The rest are semi-precious stones.
