Talc Talc Talc or talcum is a clay mineral composed of hydrated magnesium silicate with the chemical formula HMg(SiO) or MgSiO(OH). In loose form, it is (in ratio with or without corn starch) one of the most widely used substances known as baby powder. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage, and the folia are not elastic, although slightly flexible. The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 1 as the hardness of talc. Talc can easily be scratched by a fingernail. Talc
Pabstite minute fluid and solid inclusions. Its hardness is 6 on Mohs scale of mineral hardness. Its density is 4.03 g/cm and it is uniaxial. The interference colors of pabstite are anomalous blue-violet and golden yellow. The refractive indices of pabstite are ω = 1.685±0.002 and ε = 1.674±0.002 which result in low birefringence and absent dichroism. Pabstite was first described in 1965 for an occurrence in the Kalkar quarry of Santa Cruz County, California. The mineral was named for Adolf Pabst (1899–1990) a mineralogy professor at the University of California, Berkeley. Pabstite has also been reported from Tres Pozos, Baja