This piece, in near mint condition, dates from the early 1970's. Made by the W. E. Richards company, a great traditional jewelry maker from Massachusetts, it measures about 1 1/4" x 15/16".
The bezel setting holding the abalone has a very fine saw tooth/dog tooth edge to it, surrounded by a twisted wire trim. The pin mechanisms are all tight, with no play. A fold-away pendant bail, securely riveted to the mount, adds a touch of versatility, allowing it to be worn as a pendant.
The piece is marked "1/20 12kgf" and "WRE", the initials of the maker in monogram form, on an attached cartouche.