Pozzolan is named after Pozzouli, a region near Naples, Italy, which is rich in volcanic ash.
Natural pozzolan is a light siliceous mineral produced during basaltic volcanic eruptions. It contains silica, alumina and iron oxide (which gives it a red colour), as well as lime and magnesium oxide. Pozzolan is used as a cement additive.
Artificial pozzolans with the same properties as natural pozzolans can be created by heating clays, basalts or schists.