More on Ceraunium from Infoplease:

• Ceraunium - Ceraunium The opal. So called by the ancients from a notion that it was a thunder-stone. (Latin, ...
• O'pal - O'pal From the Greek ops (the eye). Considered unlucky for the same reason that peacocks' ...
• Dictionary of Phrase and Fable: C - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "C"