Carved from a piece of bone, probably sheep or cow. 9ct gold heart onlaid. 7/8" diameter. Bachelor button studs (historically called "solitaires" or bachelor's buttons) are removable, mechanical fasteners invented in the 19th century. Designed to pass through heavy, starched linens or stiff buttonholes without sewing. I read it could signal a man was unattached/available for courtship, but not sure if this is true or just a good story. This one is maybe c. 1870 - 1900? I'm not great at dating these!