Mohs Hardness Scale

Mohs Hardness Scale
Mohs Hardness Scale

National Park Service

This image contains a table relating mineral hardness for a few selected minerals with common objects that could be used to test hardness. The title, Mohs Hardness Scale is accompanied with the National Park Service arrowhead symbol. The minerals are listed from hardest to softest with their hardness scale number as follows: Diamond, 10; Corundum, 9; Topaz, 8; Quartz, 7; Orthoclase, 6; Apatite, 5; Flourite, 4; Calcite, 3; Gypsum, 2; and Talc, 1. The Common Objects for hardness comparisons are listed a column to the left as: Masonry Drill Bit, 8.5; Steel Nail, 6.5; Knife/Glass Plate, 5.5; Copper Penny, 3.5; and Fingernail, 2.5.

NPS illustration by Heather Walborn, Guest Scientist (2013-2014), NPS Geologic Resources Division.

The Mohs Hardness Scale is used as a convenient way to help identify minerals. A mineral's hardness is a measure of its relative resistance to scratching, measured by scratching the mineral against another substance of known hardness on the Mohs Hardness Scale. This graphic outlines the index minerals and some common objects that are used to determine a mineral's hardness.

This method is especially useful for identifying minerals in the field because you can test minerals against some very common objects (fingernail, a penny, a nail). The scale is named for its creator, the German geologist and mineralogist Friedrich Mohs. However, the method of comparing hardness has been used as far back as 300 BC, as mentioned by Theophrastus in his treatis On Stones.

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NPS—Geoscience Concepts

Part of a series of articles titled Fundamental Geologic Principles.

Last updated: April 12, 2023