Quite a solid 18k gold ring with a domed onyx cabochon and a centred diamond. Most probably continental European and from the second quarter of the twentieth century. The only stamp or mark is "750" for 18k gold. Somewhat remindful of Paloma Picasso's style.
Size: diameter of the cabochon :1.5 cm. ( 0 19/32" ), shank's inner diameter : 17.7mm. , total weight : 18g.
Condition : very good. What appears to be , possibly, a blemish at around " 9 o clock" on the cabochon's face is not a blemish but some reflection - has been double checked!
An eighteen carat gold ring/onyx front and centred diamond, 1925 to 1950.