The Mohs Hardness Scale is a simple but powerful system used to measure a mineral’s resistance to scratching. Developed in 1812 by German geologist Friedrich Mohs, this scale ranks minerals from softest to hardest on a scale of 1 to 10.

It remains one of the most widely used tools in geology, gemology, and mineral identification.

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How the Mohs Hardness Scale Works

The Mohs scale is based on a simple principle:

A harder mineral can scratch a softer mineral.

Each mineral on the scale can scratch the ones below it but cannot scratch those above it.

For example:

• A mineral with hardness 6 can scratch anything rated 5 or lower.
• It cannot scratch a mineral rated 7 or higher.

The scale is relative, not linear — meaning the difference in hardness between numbers isn’t equal. For instance, diamond (10) is far harder than corundum (9), even though they are only one number apart.

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The 10 Minerals on the Mohs Scale

Here are the standard reference minerals used in the Mohs scale:

Hardness	Mineral	Description
1	Talc	Softest mineral; can be scratched by a fingernail
2	Gypsum	Soft; used in drywall
3	Calcite	Found in limestone and marble
4	Fluorite	Often purple or green
5	Apatite	Found in teeth and bones
6	Orthoclase	A common feldspar mineral
7	Quartz	Very common in Earth’s crust
8	Topaz	Popular gemstone
9	Corundum	Includes rubies and sapphires
10	Diamond	Hardest natural mineral

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Why the Mohs Scale Matters

The Mohs scale helps geologists quickly identify unknown minerals in the field. It also plays a major role in:

• Gemstone grading
• Industrial material selection
• Understanding wear resistance
• Manufacturing tools and abrasives

For example:

• Quartz (7) can scratch glass.
• Diamond (10) is used in cutting tools because of its extreme hardness.

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Simple Hardness Reference Guide

You can even use everyday objects for comparison:

• Fingernail: ~2.5
• Copper coin: ~3
• Steel knife: ~5–6
• Glass: ~5.5

If a mineral scratches glass, it’s likely harder than 5.5.

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Mohs Scale vs. Other Hardness Tests

While the Mohs scale is excellent for quick identification, it isn’t precise for scientific measurements. More advanced tests, like the Vickers or Brinell hardness tests, measure hardness using exact pressure and indentation.

However, for fieldwork and basic geology education, the Mohs Hardness Scale remains unmatched for simplicity and practicality.

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Final Thoughts

The Mohs Hardness Scale is a straightforward ranking system that compares minerals based on their ability to scratch one another. Though created over 200 years ago, it continues to be a foundational tool in geology and gemology.

From soft talc to unbreakable diamond, the scale provides a clear and practical way to understand mineral hardness — and why some stones scratch while others shine.