This hat pin and others is from the  sale of the Tom Lawson collection ( author of Charles Horner of Halifax book and numerous articles on hat pins.

 A shamrock design silver hat pin set with Blue John. In good condition.   

Head  0.75 inch across  Length  of stem 6.0 inch. 

Marked Sterling . It is likely to have been made in Birmingham with the Blue John from the Derbyshire mines  C1900