Red circular stone pendant

Beautiful vibrant red circular stone/rock pendant enclosed by metal in excellent condition! I bought this from an art dealer who brought it back from Africa in 2000. It is about the size of a golf ball. I am not sure what stone it is, but it has black indentations on it and a metal loop in the back to easily make into a necklace by adding a thin chain, rope or twine. Or use it for a creative Valentine’s day gift. Thank you & enjoy!