An onyx and diamond ring, early 20th century, centring on a cushion-shaped diamond weighing

An onyx and diamond ring, early 20th century, centring on a cushion-shaped diamond weighing approximately 1.50 carats, within a border of calibré-cut onyx and outer frame of circular-cut diamonds, to scrolled shoulders, mounted in gold, size M

Central diamond measuring approximately 7.7 x 6.4 x 4.6mm, calculated weight approximately 1.50 carats, estimated colour I/J, estimated clarity SI1, medium blue fluorescence. Central diamond possibly a later replacement. Overall in good condition, some minor chips to onyx, gross weight 5 grams.