This is a very old pendant most likely of Tibetan origin, but possibly Nepalese. I believe that it depicts Lord Vishnu. The piece is inlaid with coral and turquoise and some green and brown stones that Im unsure of. I think that the pendant is possibly made of low grade silver. It is quite large, measuring 3 1/8 by 2 5/8 - it weighs 55 grams (about 2 oz). It is missing a number of surrounding stones, but the figure of Lord Vishnu is intact - please look at the photo. The piece might benefit from a bit of a clean-up, but it looks fine under normal viewing.
I would think that this piece dates to the 19th century - it is an impressive example!