DIY Mohs Field Kit
Your Interactive Guide to Mineral Hardness
Discover how to identify minerals using the Mohs scale by building a portable, low-cost test kit from everyday items. This guide makes geology accessible and hands-on.
Understanding the Mohs Scale
The Mohs scale ranks minerals by their relative scratch resistance, from 1 (softest) to 10 (hardest). A harder material will scratch a softer one. This chart shows the ten standard minerals. Note that the scale is not linear; the jump in hardness between 9 and 10 is much greater than between 1 and 2.
Hardness vs. Toughness
It’s crucial to know that Mohs hardness is only about scratch resistance. Toughness, or durability, is a material’s resistance to breaking or chipping. A mineral can be very hard but also brittle. For example, Emerald has a high hardness of 8, but its natural inclusions can make it less tough and prone to fracturing under impact.
The Golden Rule of Testing
The entire test hinges on one principle: a true scratch is a permanent groove that cannot be rubbed off. A softer item may leave a powdery smear or residue that wipes away easily. Always rub the mark to verify!
Build Your DIY Field Kit
Gather these common household and workshop items to create your portable test kit. Use the filters to sort items by their hardness range. Click on any item for more details and preparation tips.
Mastering the Scratch Test
Follow this systematic process for accurate results. The key is to narrow down the hardness range by testing with items of known hardness until you find what scratches the mineral and what doesn’t.
Prepare
Find a clean, smooth, inconspicuous area on your mineral specimen.
Select
Choose a test item from your kit. Start with one you suspect is softer than the mineral.
Scratch
Press the point of your test item firmly against the mineral and draw a short line.
Verify
Rub the mark. A true scratch is a groove. A powdery residue is just a smear.
Iterate
If it scratched, try a softer tool. If it didn’t, try a harder one.
Determine
The mineral’s hardness is between the hardest item it can scratch and the softest item that can scratch it.
Safety & Limitations
⚠️ Safety First
- Always wear gloves and eye protection when preparing kit items, especially when breaking glass.
- Store sharp items like glass shards, nails, and files securely in your kit to prevent accidental injury.
- Handle all items with care during testing.
- Responsibly dispose of any broken or worn-out materials.
ℹ️ Know the Limitations
- Your DIY kit provides a hardness range, not a precise number.
- Household items can have slight variations in hardness (e.g., different steel alloys). Use standard items for best results.
- The Mohs scale is qualitative. Distinguishing between very hard materials (e.g., 8 vs. 9) can be challenging.