You are looking at a very nice vintage 10k yellow gold ring marked psco. Which stands for Plainville Stock Co. Massachusetts. Made in the 1930's or 40's. a nice heart sheat holding a very nice green gem stone, but has some wear from age. But, very rare and hard to find. It is a 2 3/4 size. Very small for a lady with small fingers. Don't let the size full you.
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