Notable locations in Williamsburg: Williamsburg Sport Complex (A), Sport Hill Country Club (B), Iowa County Ambulance Williamsburg (C), Williamsburg First Responders (D), Williamsburg Public Library (E), Williamsburg Police Department (F), Williamsburg Fire Department (G). Display/hide their locations on the map.
Types of Opal. Opal is a hydrated amorphous form of silica; 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 the other crystalline forms of silica, which are classed as minerals.
Any kind of gemstone material can be produced as a doublet, especially expensive varieties such as sapphire, ruby and alexandrite. However, doublets are most often found in opal, since high quality precious opal is both very expensive and fragile. An opal doublet consists of a slice of precious opal usually glued to a black backing (common opal or glass), designed to imitate the appearance of a solid black opal.