" Cutting and polishing an opal is a great skill. The outer casing has to be removed with a diamond saw and then it is shaped. The Romans mastered the art thousands of years ago."
Della ran her finger over the stone. "Where did the name opal come from?"
"From the Sanskrit meaning 'precious stone,' and later the Greek derivative opallios, meaning 'a change of color'. "

― Tea Cooper , The Woman in the Green Dress