Vermiculite is a natural mineral that expands with the application of heat. The expansion process is called exfoliation and it's routinely accomplished in purpose-designed commercial furnaces. Vermiculite is formed by hydration of certain basaltic minerals. Large commercial vermiculite mines currently exist in South Africa, China, Brazil, the USA and several other countries. Structure Vermiculite is a 2:1 clay, meaning it has 2 tetrahedral sheets for every one octahedral sheet. It is a limited… (More on Vermiculite)