Beginning in the 14th Century, mourning rings were a common way to memorialize the dead. They were often paid for by the deceased, and bequeathed in wills.
They came in many forms. The molded one above is a handclasp of farewell. Many used woven hair.
The rings usually included the details of the deceased, engraved on the inside or outside of the band.
Unless the loved one was a child, or perhaps unmarried, the choice of stone was something black.
Though the original tradition died out at the end of the 19th Century, it was revived briefly in the 30s & 40s, in the form of Bakelite portrait rings.
If you want one, it’ll cost ya, but they sure are lovely.