This monogram is from the heraldic artist AA Turbayne, as featured in his book Monograms & Ciphers, London, England, (1906). 

Monogram: GHG

Accents/Accessories: Round shape; Hidden attached bail on reverse of the piece; Cut out and applied monogram; Detailed background; Heavily oxidized

Size: 50.80 x 45.72 millimeters (2 x 1.80 inches)

Weight: 33.60 grams (1.19 ounces)