Mohs' hardness scale

Description

An empirical scale used to approximate the hardness of minerals. The scale, developed by Friedrich Mohs, is based on the ability of one material to scratch another. The Mohs' hardness scale originally ranged from 1 (soft) to 10 (hard) but has recently been expanded to 15 by Ridgeway to include synthetic abrasives.

Original scale:

1. talc-easily scratched by the fingernail;

2. gypsum-just scratched by the fingernail;

3. calcite-scratches and is scratched by a copper coin;

4. fluorite -not scratched by a copper coin and does not scratch glass;

5. apatite -just scratches glass and is easily scratched by a knife;

6. orthoclase-easily scratches glass and is just scratched by a file;

7. quartz-not scratched by a file;

8. topaz;

9. corundum;

10. diamond.

Extended scale:

7. silica;

8. quartz;

9. garnet;

10. topaz;

11. fused zirconia;

12. fused alumina;

13. silicon carbide;

14. boron carbide;

15. diamond

Synonyms and Related Terms

Mohs hardness scale (sp); escala de Mohs (Port.); échelle de Mohs (Fr.)

Comparisons

Properties of Common Abrasives

Sources Checked for Data in Record

• ASTM, Standard Terminology of Microscopy, Annual Book of ASTM Standards, Section 14, General Methods and Instrumentation, ASTM, E175, 75-78, May 1982

• G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 940

• Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982

• Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976