Mohs Hardness Scale: Chart & 3-Step Field Test

The Mohs hardness scale ranks mineral scratch resistance from 1 (talc) to 10 (diamond). Compare an unknown mineral with identified references, record what scratches what, and use the result alongside other clues. A hardness result is a clue, not a mineral name.

What hardness tells you

Scratch resistance can help separate similar-looking minerals. Keep it distinct from toughness: resisting a scratch does not mean resisting a blow. Also, Mohs is a ranking, not a linear measurement; 8 is not twice as hard as 4. GIA explains hardness and toughness.

Mohs hardness scale chart: the 10 reference minerals

Everyday objects belong in a separate category. A fingernail is commonly listed around 2.5 and window glass around 5.5, but these are approximate comparisons. GIA lists glass at 5–6. Do not treat an arbitrary coin, knife, nail, or piece of glass as a calibrated standard.

A 3-step mineral hardness test

1. Select a mineral grain and a known reference

Choose an accessible, clean mineral surface rather than a coating. On a mixed rock, record which grain you test. Start with an identified reference from your kit; do not guess its identity from color.

2. Compare in both directions

Try a short controlled scratch with the reference, then reverse the comparison where practical. Remove residue with a damp cloth and inspect with a hand lens. Look for a groove, not just a colored line. Repeat an ambiguous test before drawing a conclusion. This follows the Mineralogical Society of America hardness method.

3. Record a range, or record uncertainty

Use additional known references to narrow the result. Write down both directions of each comparison. If the surface crumbles, the tool slips, or results conflict, write “inconclusive” rather than forcing a number. Save the specimen label with your notes for a later check.

Scratch or surface mark?

A softer material can leave residue on a harder one. A line that wipes away is not the lasting groove you need. Inspect after cleaning; avoid tracing sharp edges with a finger. Repeat gently on another suitable spot if you cannot tell.

Your pocket hardness kit

• Labeled, identified mineral references or a purpose-made hardness kit with its instructions.
• A hand lens to inspect the mark.
• Eye protection, a stable support, and a damp cloth.
• The printable card, a pencil, and specimen labels.

Keep reference minerals separated so they do not damage each other in the pouch. Plan the rest of your equipment with our first field kit guide.

Buying equipment? Our mineral identification kit comparison separates reference specimens from basic test tools and tools bundled with practice samples. Choose the package for the tests you want to learn.

Reading your results

Example: your sample scratches calcite (3), while fluorite (4) scratches the sample. Follow up with the reverse comparisons and note an approximate 3–4 bracket if the results agree. This narrows the investigation; it does not establish an identity.

For a teaching exercise, compare labeled calcite and quartz: their reference numbers are 3 and 7. Practice recognizing a groove before testing an unknown. Then add observations such as luster, cleavage, and crystal form using our rock identification guide.

Common mistakes

• Treating the entire rock as one mineral. Record the grain or surface tested.
• Guessing an exact value from a household object. Write the object and outcome instead.
• Equating a mark with a scratch. Clean and inspect it first.
• Repeating destructive tests on a display specimen. Stop and use other clues or ask a specialist.

What this test cannot settle

Hardness alone cannot establish a mineral's identity, value, safety, or collecting permission. A coating or mixed specimen can also leave you testing something other than the mineral you intended. If identification matters, keep the result provisional and seek expert help. This guide and card summarize published references; they are not a laboratory report or a claim of our own specimen testing.