The term crystal opals refers to transparent opals, that is you can see thru most of these opals or semi-translucent body Blue crystal opals are most common and if back is enhanced the crystal opal is lot brighter, but these have to be called solid enhanced crystal opal. Rarer colours are orange and hues sunset colours with red hues the rarest fire crystal colour. Most opal fields have crystal opal a sits formed with no base like potch or ironstone or sandstone and can be appreciated for their rarity and unique colour patterns Source your crystal opals direct from opal miners and opal wholesalers and dealers for your single gem crystal opal or parcel crystal opals from lightning ridge Australia