I hand cut this cabochon using natural Opal from old stock that came from the now closed Manhattan mine found around Knoxville in Napa County, CA. Measurements in the title in millimetres. This material has been called Manhattan Opal, Honey Opal, Lemon Opal and Yellow Opal. Only way to really keep track of this is to look where the material comes from. The Opal fluoresces Yellow under all UV wavelengths but is best LW. It is also phosphorescent. I got the rough for this piece from my brother Jim as a birthday present. He got the material from an old collection he bought and he is confident of its providence. A pretty rare material! The 5 pieces I made and listed are ALL that I have. If you see less than 5 in my store then the others have already sold.
Fluorescent pics are under LW UV using a Convoy UV flashlight and a simple digital camera. If you are interested in more fluorescent specimens you should contact my brother James Horste. I only dabble and I got this rough material from him as a present.
The Manhattan mine is now gone so the only place to get this material is from collections. (FL Yellow LW, MW, SW, phosphorescent blue-white)