What is Mohs Hardness? Mohs hardness is a scratch-comparison scale (1–10) used to compare how easily one mineral scratches another. It is a field test, not a lab measurement, and it works best with clean, fresh surfaces. Collectors use Mohs hardness to narrow down an ID fast when color and luster are misleading. Because weathering can soften surfaces, confirm with a second scratch on a fresh edge or broken face.
Use Mohs Hardness with a small set of reference picks (fingernail, copper coin, steel nail, glass, quartz) and write the hardest thing that scratches the target. Do the scratch on a sharp corner or a fresh break; rounded rinds and iron staining can give false results. If the mineral powders, flakes, or crumbles instead of taking a clean scratch, record that too because it affects how reliable the number is. When you’re unsure, record a range (for example, 5–6) and confirm later with streak and specific gravity.
Mohs Hardness vs. scratching a weathered rind Weathered coatings can be softer than the mineral. Scratch a fresh break or sharp edge to get a meaningful hardness result.
Mohs Hardness vs. a gouge that leaves powder A gouge can be crushing, not a true scratch. Look for a clean line cut into the surface, not just a smear of powder.
Mohs Hardness vs. hardness of the host rock Make sure you’re scratching the mineral itself, not the surrounding matrix, cement, or a different grain.
Mohs Hardness vs. “it scratched glass so it’s quartz” Many minerals can scratch glass. Use hardness as one clue alongside luster, streak, and cleavage.