He goes on to recount how the allure of emeralds and rubies is provided by chromium , which not only colours the stones but also fluoresces with red light , so that the best gems appear to flicker with inner fire .
Nocturnal crawler , a scorpion remains well camouflaged under a flash-light 's beam , but fluoresces in ultraviolet light [ as seen here ] , a reaction that remains a mystery to scientists .
