Ten reference minerals, softest to hardest. If specimen A scratches specimen B, A is harder — that simple idea has organized mineralogy since 1812.
Friedrich Mohs ranked minerals by a single question: which one scratches which? The result is an ordinal scale — the gap between 9 and 10 is far wider than between 1 and 2 — but it’s still the fastest identification tool in the field kit. Click any reference mineral for its full entry.
No reference set handy? Everyday objects bracket the scale:
Scratches talc and gypsum.
Scratches calcite.
Scratches fluorite, apatite; stopped by feldspar.
Quartz and harder leave a mark.
Bites orthoclase; slides off quartz.
Unglazed porcelain — anything harder can’t be streak-tested.
Open the hardness browser → to see every catalogued mineral at each step of the scale.