Smoky Blue Roman Lady's head cameo in box

(Michigan)

My husband received a cameo in it's original box from his grandmother. We do not know much about it. It is all a smoky blue color and depicts a female roman head. She is facing right, has curly hair and appears to have a headband carved just under the hairline on the forehead. It is still in it's original jewelers box. The cameo was purchased from Salle Jewelry Co., 407 E Genesee Ave, Saginaw, MI. I do not know if they made the cameo or if it was just purchased there, however, the box is cardboard and made to fit the oval shaped cameo. We have no idea what this might be made of. It is one solid piece, nothing attached. I am not able to take a picture now, but wondered if you would be able to give us any indication of what it may be made of from this description. I was debating on putting it in a setting for a pendant, however, I hesitate to do that since it is a cameo in a box and has never been mounted in a setting. If there is any value to it, it may reduce the value of it by mounting it in a setting now. The face of it is in perfect condition. Can you give me any possible information on this by the description?