Cloudy

This is an effect often seen in gems such as  Diamonds  and  Emeralds,  which  is  normally  caused by a mass of small inclusions, often of a  fibrous nature.

Not only does it diminish the appearance of the  gem, but it also reduces its ability to demonstrate  brilliance and dispersion (also known as fire).  Almost  without  exception,  cloudy  gems  are  less valuable than a clear gemstone of a similar colour, cut and carat weight.