Malachite? Yes, a beautiful geen coloured mineral that forms deep inside the earths alongside copper with beautiful ring shapes inside, called peacock's eyes. Neat hey?
Malachite, being a naturally formed material will have variations in colour and and patterns - Your ring will be one of a kind, with your own special piece of earth, green and lustrous, protected by a tungsten carbide inner, polished to a shine and comfy smoothness.