What Exactly are Inclusions?
In geology an inclusion is any material that becomes trapped within a rock or a mineral during its formation. In gemmology an inclusion is a characteristic that's either enclosed within a gemstone or which reaches the surface from the inside.
Although inclusions in rocks minerals and gemstones are often other minerals they may also be water, gas or petroleum and in the case of amber, insects or plant matter. With that said amber is neither a rock or a mineral because it's fossilsed tree resin.
Inclusions are one of the most important factors when determining a gemstone's value. Whilst in some they affect clarity which can affect the value of a stone, in others such as star rubies and sapphires and varieties of included quartz the inclusions are the very reason why the value increases.