mohs hard·ness scale | ˈmōz ˈhärd-nəs skāl
A qualitative scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material
The Mohs hardness scale ranges from 1 to 10. It includes: Talc (1), Gypsum (2), Calcite (3), Fluorite (4), Apatite (5), Orthoclase (6), Quartz (7), Topaz (8), Corundum (9), Diamond (10).
The scale was created by Friedrich Mohs in 1812.