Mexican Fire Opal Necklace

This glowing necklace has three Mexican fire opal cabochons, a large central one flanked by two smaller ones, each a "boulder" type with precious opal in matrix.  Each is bezel-set in sterling silver with an open back.  The cabochons are oval;  the central cab is about 15 x 22 x 7mm (0.6 x 0.9"), and the side cabs about 14 x 17 x 7mm (0.6 x 0.7").  The necklace is about 18" and fastens with a lobster clasp.