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Mohs Hardness Scale: Chart & Scratch Test Tool

The Mohs hardness scale ranks relative scratch resistance from talc at 1 through gypsum, calcite, fluorite, apatite, orthoclase feldspar, quartz, topaz, corundum, and diamond at 10. A higher index mineral can scratch a lower one, but the numbers are ordered ranks rather than equal units. GeoMiner's private browser tool estimates a broad hardness range from two observations: the hardest reference an unknown specimen scratches and the softest reference that scratches the specimen. Approximate field references include a fingernail near 2.5, clean copper near 3, ordinary window glass near 5.5, and verified quartz at 7. Reference objects vary, so users should confirm a persistent groove rather than loose powder, repeat both directions with light pressure, and combine hardness with lustre, streak, cleavage, habit, density, and geologic context. Do not destructively test valuable, fragile, fibrous, dusty, radioactive, arsenic-, mercury-, or lead-bearing candidates. Hardness is not toughness, and scratching glass does not prove a specimen is diamond.

Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

  • Mohs Hardness Scale — U.S. National Park Service. Index minerals, scratch-resistance definition, and common field references.
  • Mohs Hardness Scale — U.S. Geological Survey. Public-domain educational scale showing the ten index minerals and common testing tools.
  • Hardness identification activity — British Geological Survey. Classroom scratch-testing sequence, observations, and interpretation guidance.
  • More than the Mohs Scale — Gemological Institute of America. Explains the scale's non-linear nature and the distinction between hardness, toughness, and stability.

Read GeoMiner's editorial methodology.

Common questions

What does the Mohs hardness scale measure?
It ranks relative scratch resistance. A harder reference can scratch a softer mineral. It does not directly measure strength, toughness, cleavage, or resistance to impact.
Is the Mohs scale linear?
No. The numbers are an ordered comparison, not equal units. The measured hardness gap between diamond and corundum is much larger than one number suggests.
Does scratching glass mean a specimen is diamond?
No. Many common minerals at about Mohs 5.5 or harder can scratch ordinary glass, including feldspar and quartz. Identification requires several independent properties.
Can I use a coin for a mineral hardness test?
Coin composition varies by country and year. A known piece of clean copper is a more honest approximate reference, and calibrated hardness picks are better when precision matters.
Should I hardness-test every unknown specimen?
No. Avoid destructive testing on valuable, fragile, fibrous, dusty, radioactive, arsenic-, mercury-, or lead-bearing candidates. Begin with non-destructive observations and use qualified help where consequences matter.

JavaScript is loading the interactive GeoMiner experience. The identification tools provide educational candidates, not laboratory confirmation.