Unusual Oak Leaf Pin.

I believe it is gold plated with a black overlay. I wouldn't exactly call it enamel. More painted on.

It has a faux pearl with worn finish and a clear crystal. I don't think it is a diamond. 

The prong set is professional. It is good quality.

The clear stone has a chip or crack only seen under magnification.

Measures 2" by 1 3/8" approx.

I'm not sure of the age. I've had it for about 20 years.