Earth Science: Mohs Hardness Scale from 1 to 10 Practice
Using scratch tests to compare mineral hardness
Earth Science: Mohs Hardness Scale from 1 to 10 Practice
Using scratch tests to compare mineral hardness
Earth Science - Grade 9-12
- 1
Rank these minerals from softest to hardest: quartz, talc, fluorite, diamond, calcite.
Match each mineral to its number on the Mohs scale, then order the numbers from least to greatest.
The minerals ranked from softest to hardest are talc, calcite, fluorite, quartz, and diamond. Their Mohs hardness values are 1, 3, 4, 7, and 10. - 2
A mineral scratches calcite but does not scratch fluorite. What is the likely hardness range of the mineral?
If a mineral scratches another mineral, it is harder than that mineral.
The mineral is harder than calcite, which has a hardness of 3, but softer than or equal to fluorite, which has a hardness of 4. Its likely hardness is between 3 and 4, or about 3.5 to 4 if it cannot scratch fluorite. - 3
A student tests an unknown mineral. It is scratched by a copper penny, but it scratches a fingernail. A fingernail has hardness about 2.5 and a copper penny has hardness about 3. What is the best estimate for the mineral's hardness?
The mineral's hardness is greater than 2.5 because it scratches a fingernail. It is less than 3 because it is scratched by a copper penny. The best estimate is about 2.5 to 3. - 4
Explain why diamond can scratch quartz, but quartz cannot scratch diamond.
Compare the hardness numbers of diamond and quartz.
Diamond can scratch quartz because diamond has a Mohs hardness of 10 and quartz has a Mohs hardness of 7. A harder mineral can scratch a softer mineral, so quartz cannot scratch diamond. - 5
A mineral sample scratches apatite and is scratched by quartz. What can you conclude about its hardness?
The mineral is harder than apatite, which has a hardness of 5, and softer than quartz, which has a hardness of 7. Its hardness is likely between 5 and 7. - 6
A mineral can scratch glass but cannot scratch quartz. Glass has a hardness of about 5.5 and quartz has a hardness of 7. What is the likely hardness range of the mineral?
Use both test results to set a lower limit and an upper limit.
The mineral is harder than glass, so its hardness is greater than 5.5. It cannot scratch quartz, so its hardness is less than or equal to 7. The likely range is greater than 5.5 and up to 7. - 7
Two minerals are tested against each other. Mineral A scratches mineral B, but mineral B does not scratch mineral A. Which mineral is harder, and how do you know?
Mineral A is harder. A mineral that scratches another mineral has a higher hardness than the mineral it scratches. - 8
A mineral has a Mohs hardness of 6. Name one reference mineral it should scratch and one reference mineral that should scratch it.
Choose one mineral below 6 and one mineral above 6 on the Mohs scale.
A mineral with hardness 6 should scratch apatite, which has hardness 5. It should be scratched by quartz, which has hardness 7. - 9
A geologist finds that an unknown mineral scratches gypsum, calcite, and fluorite, but does not scratch apatite. What is the best estimate of the mineral's Mohs hardness?
The mineral is harder than fluorite, which has hardness 4, but it does not scratch apatite, which has hardness 5. The best estimate is between 4 and 5. - 10
Why is the Mohs hardness scale considered a relative scale rather than a scale with equal-sized intervals?
Think about whether each step on the scale represents the same amount of hardness change.
The Mohs scale is relative because it ranks minerals by what they can scratch, not by equal numerical differences in actual hardness. The difference in hardness between 9 and 10 is much greater than the difference between many lower numbers. - 11
A mineral scratches orthoclase feldspar but is scratched by topaz. Orthoclase feldspar has hardness 6 and topaz has hardness 8. Which Mohs reference mineral has a hardness between those two values?
Quartz has a hardness of 7, which is between orthoclase feldspar at 6 and topaz at 8. The unknown mineral may have a hardness near quartz. - 12
A student claims, 'A mineral with hardness 8 is twice as hard as a mineral with hardness 4.' Explain why this statement is not correct.
The numbers show rank order, not exact ratios.
The statement is not correct because the Mohs scale is not a proportional scale. A hardness of 8 means the mineral can scratch minerals with lower Mohs numbers, but it does not mean it is exactly twice as hard as a mineral with hardness 4.