Black agate set in stainless steel looks like onyx size 6 and beautiful ring

This is a ring that I bought at a boutique and they really did not know whether it was agate or onyx. to be safe and not mislead I am say agate size 6 with thick stainless steel because it is not marked it is a beautiful ring I bought it and never wore it it was so large it is an inch long a beautiful ring thanks for looking