Light opal is opal ith a light bodytone in the range N7 to the lightest N9. This category also includes most transparent pure crystal opal but if the amount of “fire” or colour play in the opal is really rich and dense the crystal opal may rightly be termed a dark opal. Body tone refers to the darkness of the body of the opal looking down on the face as it would be set. There may be “black” on the back of an opal but if a lighter layer is behind the face of gem crystal the view from the front is what determines the body tone scale N1 to N9.