Here's how it works:
* Fingernail: Has a hardness of about 2.5 on the Mohs scale.
* Copper Penny: Has a hardness of about 3.5 on the Mohs scale.
* Steel Nail: Has a hardness of about 5.5 on the Mohs scale.
The Process:
1. Try to scratch the mineral with your fingernail.
* If the fingernail scratches the mineral, the mineral's hardness is less than 2.5.
2. If the fingernail doesn't scratch it, try scratching it with the copper penny.
* If the penny scratches the mineral, the mineral's hardness is between 2.5 and 3.5.
3. If the penny doesn't scratch it, try scratching it with the steel nail.
* If the steel nail scratches the mineral, the mineral's hardness is between 3.5 and 5.5.
4. If the steel nail doesn't scratch it, the mineral's hardness is greater than 5.5.
Important Considerations:
* Real Scratch vs. Streak: Make sure you're observing a real scratch, not just a streak of material left behind from the testing tool. A streak can be wiped away.
* Surface Condition: The surface of the mineral can affect the test. A weathered or altered surface may be easier to scratch than the fresh, unweathered material underneath.
* Consistency: It is best to use the sharpest point to try and perform the scratch.
* Mohs Hardness Scale: This is a relative scale, meaning it only tells you the relative hardness of minerals compared to each other. The difference in absolute hardness between minerals can vary significantly.
* Other Factors: This is a simple field test and is not a precise measurement of hardness. Other tests can be used for a more accurate assessment.
In summary, the fingernail/penny/nail test is a quick and dirty way to estimate a mineral's hardness relative to those common objects.