Perhaps this was meant to be a memorial ring? That's what the black enamel is hinting at, but there's no dedication. The dots are unusual, and the old mine cut diamond is bright. How strange: I wouldn't say no to this piece being an engagement ring. 18k gold, c. 1880.
MATERIALS: 18k gold (marked), black enamel, .15ct old mine cut diamond
AGE: c. 1880
CONDITION: Very good - some minor loss to the enamel in a few places
SIZE: 5.75, resizing not recommended; 6.5mm head, 2mm shank