Mohs Scale
Definition
A scale of mineral hardness from 1 (talc) to 10 (diamond), created by Friedrich Mohs. Each mineral can scratch those below it on the scale.
Example
The Mohs scale: 1-Talc, 2-Gypsum, 3-Calcite, 4-Fluorite, 5-Apatite, 6-Orthoclase, 7-Quartz, 8-Topaz, 9-Corundum, 10-Diamond.
Measuring Mineral Hardness
The Mohs Scale of Mineral Hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in materials science.
The 10 Reference Minerals
- Talc (Softest - feels greasy)
- Gypsum (Can be scratched by fingernail)
- Calcite (Scratched by copper coin)
- Fluorite (Scratched by knife)
- Apatite (Scratched by glass)
- Orthoclase Feldspar (Scratches glass)
- Quartz (Scratches steel)
- Topaz (Harder than quartz)
- Corundum (Ruby/Sapphire)
- Diamond (Hardest natural material)
Practical Use
The scale is ordinal, meaning distinct steps. Diamond (10) is exponentially harder than Corundum (9), not just 10% harder. In the field, geologists use common objects like a fingernail (2.5), a copper penny (3.5), a steel nail (5.5), and a streak plate (6.5) to estimate hardness.