Dendritic Opal:  FL Blue-White SW Hyalite Opal:  FL Green SW This specimen comes from Cedar Rim, a place about 35 miles from Riverton, Wyoming.  The fluorescent color of the hyalite opal is from uranyl ion, one of the few activators that always fluoresces the same color. I don't know what the activator is in the blue-white fluorescing material. The color scheme is reminiscent of willemite and margarosanite from Franklin, though the dendritic opal does not fluoresce quite as brightly as most margarosanite. The specimen's display face is about 3 1/4 x 1 1/2 inches. Opal is a type of amorphous, hydrated silica.  In other words, it doesn't have a regular crystal structure.  Its empirical formula is essentially the same as silicic acid, H2SiO3.   In the case of opal it's written as SiO2 nH2O.