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
Faustite Faustite The IMA approved mineral faustite, named after the American mineralogist and petrologist with the U.S. Geological Survey (USGS) Dr. George Tobias Faust, is a member of the triclinic turquoise group of hydrous phosphates with the following chemical composition: ZnAl(PO)(OH)·4HO Some divalent copper generally replaces the zinc position. Faustite is the zinc rich analogue of turquoise having almost four times as much zinc than copper in its crystal structure. Trivalent (ferric) iron may replace some of the aluminum. Minor amounts of calcium may also be present. It has a hardness of 4.5 - 5.5 on the Mohs scale of mineral