Proper noun

1. from the precious stone, invented in the nineteenth century.
   • 1985 Alice Munro, The Progress of Love, Chatto&Windus 1987, ISBN 0701131616, page 208:

     Perhaps to console herself for the bad luck she had already suffered, in a back corner of South Sherbrooke Township - or perhaps to make up, ahead of time, for a lack of motherly feelings - she gave the girls the fanciest names she could think of: Opal Violet, Dawn Rose, and Bonnie Hope.

2. A type of petrol made by the BP company designed to be unable to used for petrol sniffing. (Reference: BP article on Opal http://www.bp.com/sectiongenericarticle.do?categoryId=9008933&contentId=7016884.)