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
Chalcocite Chalcocite Chalcocite (), copper(I) sulfide (CuS), is an important copper ore mineral. It is opaque and dark-gray to black with a metallic luster. It has a hardness of - 3 on the Mohs scale. It is a sulfide with an orthorhombic crystal system. The term chalcocite comes from the alteration of the obsolete name "chalcosine", from the Greek "khalkos", meaning copper. It is also known as redruthite, vitreous copper and copper-glance. Chalcocite is sometimes found as a primary vein mineral in hydrothermal veins. However, most chalcocite occurs in the supergene enriched environment below the oxidation zone of copper deposits as