Material: Available in 18k or 14K Gold - Gold Natural Moss Agate Ring. Moss agate is truly a gemstone unlike any other. It has a beautiful marbled green effect on its surface. No two moss agate stones are the same, making each and every one unique. WHAT IS MOISSANITE? Moissanite is a diamond simulant made of silicon carbide. A diamond simulant is a stone that has a similar appearance to a diamond but is not a real diamond. It is very difficult to tell apart a diamond & moissanite, making moissanite a common diamond alternative.