Gemstones come from many sources and are comprised of different things. A gem can be a rock, a mineral, or organic matter. The main factor in elevating a rock, mineral, or biogenic substance to gemstone status comes down to two fundamental factors: rarity and beauty.
A gemstone (also called a gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal.
Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow) and morganite (pink), which are all varieties of the mineral species beryl. In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology.