I love these specimens! The opal has a faint yellow green hue to it, and like most hyalite specimens, is strongly fluorescent under UV light. What sets these apart is the presence of trace amounts amounts of the Uranyl (UO2) molecule, which causes daylight fluoresence. These hit the market a few years ago, and people soon realized there was more value in them as jewlrey rather than specimens, making good pieces hard to come by.