Talc, hydrous magnesium silicate, is the softest known mineral and is number 1 on the Mohs hardness scale. When ground up into fine particles, it is sold as 'talcum powder' and used as a drying agent. It forms as an alteration product of other silicates in localities worldwide. Talc is usually massive or 'foliated' (in sheets) and has a pearly luster and a 'soapy' or greasy feel. The material found in digging the Hoosac Tunnel in Massachusetts is extremely typical of the species.