A stone’s clarity refers to how much inclusion a gemstone contains. An inclusion is the presence of any material that is not a part of the mineral or gemstone. Many inclusions are colorless. While stones with some inclusion may be graded decently for having good character, stones that are too heavily included will not receive high grades. Gemstones are described as free of inclusions, very lightly included, lightly included, moderately included, heavily included, or excessively included.