Crystal Opal is a name for an opal with a transparent to translucent body. Normally, only a stone with good play of colour is called by that name. Transparent stones with weak or no fire are normally termed as jelly or water opals.
Chemically these stones are cleaner form of opal as the pure silica is transparent. Opal body colour of other varieties is caused by trace elements in their structure.
Crystal Opal is mined in many places. All Australian deposits have some amount crystal opal coming out of them. Mexico, best known for its fire opal, produces some amazing stones with a crystal body. Ethiopian Welo region also has a significant production of this type of gem that is sometimes faceted to reveal an amazing, flickering fire.
Crystal Opal is valued for its 3-dimensional play of colour, clearly visible due to the transparent body. The best examples of these gems are literally filled with strong fire, dancing with a slightest move. While it is true that transparent body doesn’t give good contrast to the play of colour, the sort of the black opal enjoys, it can easily be set in a jewel with a closed back that will give it a dark tone to further enhance its looks. This type of opal is perfect material for carvings. With transparent body we can enjoy its whole form, just like you would with a glass sculpt.