Peruvian Blue Opal

Peruvian opal (also called blue opal) is a semi-opaque to opaque blue-green stone found in Peru, which is often cut to include the matrix in the more opaque stones. It does not display play of color.
High quality blue opal is sold for several thousand dollars per kilo as rough stone.
Opal is a hydrated amorphous form of silica (SiO 2 ·nH 2 O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.