Hyalite Opal On Matrix From Mexico- Collectors Piece, Home Décor, Statement PieceHyalite Opal On Matrix From Mexico Collectors Piece, Home Dcor, Statement Piece Weight 155g Size 8cm by 4cm Thickness 3cm Hyalite Opals occur in volcanic and magma created igneous rock formations. Water and silica were introduced into the rock formations when they were still very hot and formed globular and irregular crusts as they cooled. The water dehydrated and the silica left a gel which solidified over millions of years. Hyalite is a form of opal