Material: S925 Sterling Silver Synthetic Ruby (Verneuil method) Stone Size: 6mm round faceted cut Size 9 (Inner diameter 15.7mm) This piece uses synthetic ruby, which has the same chemical composition and structure as natural ruby. While it is much cheaper compared to natural stones, it retains the excellent "luster," "brilliance," and "durability" of ruby. Also, ruby refers to a specific color variety of the mineral "corundum," which is the same mineral as sapphire.