Crystal Opal is a term to describe an opal with a transparent to translucent body. Normally only a stone with good play of colour can be called a Crystal Opal, those with weak or no fire are normally termed as Jelly or Water Opals. Chemically these stones are clearer form of opal as the pure silica is transparent and an opal body colour of other varieties is caused by trace elements in their structure. Crystal Opals are mined in many places- all fields of Australia have some 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 crystal opals that are sometimes faceted to reveal an amazing dancing fire. Crystal Opals are valued for their 3-dimensional play of colour that is clearly visible in transparent opal body. The best examples of these gems are literally filled with strong fire that is dancing with a slightest move. Another nice featureof these opals lies in their transparency. While it is true that transparent body doesn't give a 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 enchance its fire. Crystal Opal is also a good material for carvings as the whole shape (front and back) can be enjoyed and used for optical effects.