The Mohs' Hardness Scale

A good property in mineral identification is one that does not vary from specimen to specimen. In terms of reliability, hardness is one of the better physical properties for minerals. Specimens of the same mineral may vary slightly, but generally they are quite consistent. Inconsistencies occur when the specimen is impure, poorly crystallized, or actually an aggregate and not an individual crystal.

Hardness is one measure of the strength of the structure of the mineral relative to the strength of its chemical bonds. Hardness is generally consistent because the chemistry of minerals is generally consistent.

Hardness can be tested through scratching. A mineral can only be scratched by a substance harder than itself. A hard mineral can scratch a softer mineral, but a soft mineral cannot scratch a harder mineral (no matter how hard you try). Therefore, a relative scale can be established to account for the differences in hardness simply by seeing which mineral scratches another. That is exactly what French mineralogist Friedrich Mohs proposed almost one hundred and seventy years ago. The Mohs' Hardness Scale, starting with talc at number 1 and ending with diamond at number 10, is universally used around the world as a way of distinguishing minerals. Simply put—the higher the number, the harder the mineral.

GeoGallery Link	Scale No.	Mineral	Common
n/a	1	Talc	Fingernail
	2	Gypsum	Fingernail
	3	Calcite	Penny
	4	Fluorite	Window glass/knife blade
n/a	5	Apatite	Window glass/knife blade
	6	Orthoclase	Steel file
	7	Quartz
n/a	8	Topaz
n/a	9	Corundum
n/a	10	Diamond