Here we have a fine and typical specimen of Hyalite Opal (Opal-AN) from the well known Czech locale Valeč of Karlovy Vary Region. Hyalite is a colourless variety of Opal and also an amorphous silica-glass, containing about 3-8% water. Because it has a different structure, it does not show the opalescence (play of colour) that is found in precious Opal. Valeč is a famous locality for Opal-AN (Hyalite) exploited since the 19th century. The specimens from this locality are part of many world museum collections. Nowadays it is a military area and also a nature preserve.