What kind of blue green clear stone glows neon when held under black light?

I have an emerald cut stone, which is clear, blue green ( but jewelers have told me it is NOT an aquamarine ) and when it is held under a black light, it glows neon green. Nobody can tell me what it is; I thought perhaps aventurine? Any ideas?
Update: Not sure if it IS fluorite or not; it's in a ring that's about 100 years old, and I thought it came from California. Just curious, heirloom, you know?
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