What are the characteristics and classification of gemstones? Gemstones are made of various materials. Most gemstones are from natural minerals, which means they are naturally occurring, each with a particular chemical composition and crystalline structure. In terms of chemical composition, the largest group of gemstones consists of silicates, and the next largest group contains oxides. below you will find some information about most gemstones. For Information On Any of The Below Listed Gemstones Please click on the appropriate gem you would like more information about.