Hi Mike thanks for writing in. Unfortunately the photo of the antique locket didn't come through. It sounds beautiful from your description. You are welcome to attach a photo in a follow up submission if you like.
Gold lockets were extremely popular on both sides of the pond in the 1800s especially towards the latter half of the century, after 1860's when the civil war started in the United States. The percentage of gold used in this piece, will provide dating clues and although you mentioned the hallmarks are worn away, you can test the gold yourself with gold testing equipment and it will not only register if the piece is gold but will also identify the carat.
The gold content of English jewelry can help you date it. In England before 1854, gold meant high carat gold, like 18 carat plus. In that year, in 1854, however, 15, 12 and 9 carat gold were legally recognized. The point is, if the gold is 15, 12 or 9 carat the locket will be dated after 1854.
