Simply put, an inclusion is any material that is trapped inside of another mineral while that mineral forms.
In gemology, inclusions are actually quite important in studying the stones and come quite handy identification, differentiation and evaluation purposes. are not always a negative feature. Some inclusions can enhance the beauty or add to the mystery of a gemstone; it is the inclusions that create stars in asterism gemstones and the flash in moonstone. Inclusions can identify a gem or indicate its origin, even add to its value. In diamonds each flaw or blemish lowers its clarity grade, hence lowers its value. In rubies and sapphires, inclusions may pinpoint where the stone was mined or whether it was heated.