Large Boulder Opal Sterling Silver Ring Vintage c1980
The silver mark can be found to the rear, this is a little rubbed but you can make out the '.925' for sterling silver.
Size UK K, US 5.5 or internal diameter 1.6 cm or 0.6 inches.
Size of head 4.8 x 2.5 cm or 1.9 x 1.0 inches.
Weight 44.6 grams or 28.7 penny weight.