Mohs Hardness Estimator
Run a few simple scratch tests against everyday reference tools and narrow your specimen down to a Mohs hardness range, with the scale’s index minerals that fall inside it.
Estimated hardness
Run at least one scratch test below.
How the scratch test works
Friedrich Mohs built his 1812 hardness scale on a simple rule: a harder mineral scratches a softer one, and a softer mineral never scratches a harder one. A field kit substitutes common objects for a few points on that scale — a fingernail sits around 2.5, a copper penny around 3.5, glass or a steel knife blade around 5.5, and a steel file around 6.5 — so testing your specimen against each one brackets its true hardness between whichever tools scratch it and whichever tools it scratches.
Test on a fresh, unweathered surface: a dull or coated face can give a false result, and testing along a cleavage plane can make a mineral seem softer than it is because you’re splitting it rather than scratching it. If a test is ambiguous, try it again on a different spot before recording the result.
Frequently Asked Questions
What is the Mohs hardness scale?
The Mohs scale ranks mineral hardness from 1 (talc) to 10 (diamond) using ten reference minerals. Each one scratches every mineral below it on the scale and is scratched by every mineral above it. It measures scratch resistance only, not toughness — a hard mineral can still be brittle and shatter easily.
What tools does a field scratch test actually use?
A common substitute kit uses a fingernail (about 2.5), a copper penny (about 3.5), glass or a steel pocketknife blade (about 5.5), and a steel file (about 6.5). Testing a specimen against each one brackets its hardness between the tools that scratch it and the tools it scratches.
Why does the result come back as a range instead of one number?
A field kit only gives you a handful of reference points, so the best you can determine is that the specimen sits between two of them — for example, harder than a penny but softer than glass. A tighter range needs a calibrated hardness pick set with more reference points.
Can two different minerals have the same hardness?
Yes. Hardness alone rarely identifies a mineral uniquely — several common minerals cluster around the same values. Pair a hardness range with color, streak, luster, cleavage, and specific gravity for a more confident identification.
Educational field tool only, not a certified mineral identification, gemological appraisal, or investment guidance. For a definitive ID of an unusual or valuable specimen, consult a qualified mineralogist or accredited laboratory.