Ring with crystal opal and brilliant-cut diamond approx. 0.06 ct (hallmarked),

Ring with oval crystal opal ca. 3 ct, beautiful colours, with slight fractures and slightly loose and brilliant-cut diamond ca. 0.06 ct (marked), 18K yellow gold, 10.7 g, ring size 58, late 20th century, signs of wear, unknown maker's mark, solid workmanship.