mid-late 1800's solitaire pearl ring -I've never seen a pearl like this

This belonged to my Great great Aunt Julia; she was born in the mid 1800's, was from New York and traveled to Colorado escorting my 15 year old Grandfather in 1885-

The ring is not marked that I can see, but untarnished after all these years. The band is two strands with three faint interior bracings between the bands.
The pearl has a slight opaline iridescence in the light and a faintly yellowish area on one side.

Can you tell me anything about this ring?