A gem is a fine, precious or ornamental stone.
Raw stone torn from the ground by the miner, a gem is often cut by the lapidary to end up mounted on a ring, in an earring or any other jewelry ornament. It can be natural, processed or artificially manufactured (synthetic stone).
Few gems are perfectly pure. Most contain foreign objects or have various crystallization accidents. These accidents are considered inclusions, which should not be described as "defects" because their presence does not necessarily result in a depreciation of the gem.
Inclusions follow strict laws and may provide information on the formation and types of deposits of precious, fine or ornamental stones.
These are identification characteristics: each gem has its own inclusions. Inclusions are relatively common in minerals; they are either of the same species (inclusion of diamonds in diamonds, for example) or foreign (inclusion of gold in quartz, for example). As small as they are, inclusions can provide valuable insights into the formation of the surrounding crystal, called the "host crystal."
The minerals included may be older than it, and have been simply encompassed during growth. They may also have formed at the same time as the host crystal, which, following faster growth, has included them in its mass. There are also inclusions that are more recent than the host crystal: they come from liquids that have been introduced through cracks in the crystal.