Mineral necessarily constant for all sides, which is a function of its structure; crystallographic weakness renders some directions softer than others. An example of this property exists in kyanite, which has a Mohs hardness of 5½ parallel to [001] but 7 parallel to [100]. The most common scale of measurement is the ordinal Mohs hardness scale. Defined by ten indicators, a mineral with a higher index scratches those below it. The scale ranges from talc, a phyllosilicate, to diamond, a carbon polymorph that is the hardest natural material. The scale is provided below: Lustre indicates how light reflects from the mineral's
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