Geological Mohs Mineral Scratch Hardness Test
A challenging, hands-on discovery and STEM project designed for curious young minds aged 10 to 14.
Materials Needed
- • Diverse mineral and rock specimens (field collected or geological kit) (6 specimens)
- • Pre-1982 copper penny (Hardness 3.5) (1 unit)
- • Steel nail or pocket knife edge (Hardness 5.5) (1 unit)
- • Unglazed porcelain tile or back of ceramic mug (for streak test) (1 unit)
- • Glass slide or scrap glass piece (1 unit)
Pro Tips
- → Explain testing tools on the Mohs scale: Fingernail = 2.5, Copper penny = 3.5, Steel nail = 5.5, Glass plate = 5.5–6.0.
- → A mineral can only scratch materials softer than itself, and can only be scratched by harder materials.
- → Wipe away loose dust after each scratch test to confirm an actual physical groove was cut into the surface.
Safety First
Do not press hard on the glass slide; place the glass flat on a table during scratch testing.
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Step-by-Step Instructions
Step 1
Assemble 6 diverse stone and mineral specimens (e.g., quartz, calcite/chalk, slate, granite, gypsum).
Step 2
Test each specimen with a fingernail (Hardness 2.5): if scratched, log hardness as <2.5; if unscratched, test with a copper penny (3.5).
Step 3
Test remaining specimens with a steel nail (5.5) and scrape against an unglazed glass plate (6.0), logging which surfaces scratch.
Step 4
Rank all 6 specimens in order from softest to hardest and consult a geological guide to verify mineral identities.