My guess is that it is a Mexico 1/2 real 1834-42 Guanajuato mint (assayer PJ) that somebody cut in half.
In this shape it should weigh about 0.7 gm, the diameter, or wide part, should be about 16 mm.
In this shape it should weigh about 0.7 gm, the diameter, or wide part, should be about 16 mm.



















