The Mohs scale is a practical way to compare how resistant minerals are to scratching. It is especially useful for making rough mineral identifications in the field, though it is not a precise measure of how a material will perform in industrial settings.
The Mohs scale of mineral hardness is a qualitative, ordinal scale from 1 to 10. It describes a material's scratch resistance: a harder material can visibly scratch a softer one. The scale does not directly measure properties such as toughness, resistance to breaking, or overall durability.
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What is the Mohs scale?
A qualitative, ordinal scale from 1 to 10 that ranks minerals by their resistance to visible scratching.
How does a Mohs scratch comparison work?
A harder material can visibly scratch a softer one. Comparing a sample with reference materials helps place its hardness between or at reference values.
What does it mean that the Mohs scale is ordinal?
The numbers establish a ranking, but the gaps between them are not equal amounts of absolute hardness.
Who introduced the Mohs scale, and when?
German geologist and mineralogist Friedrich Mohs introduced it in 1812. Scratch comparisons themselves were described much earlier by Theophrastus and Pliny the Elder.
Name two limitations of the Mohs scale.
It is not a precise measure of absolute hardness or a reliable predictor of industrial durability. It can also be difficult to assign one value to a rock made of minerals with different hardnesses.
Quiz questions
What property does the Mohs scale primarily compare?Answer: Resistance to being visibly scratched by another material.
What does it mean if a sample is scratched by apatite but not by fluorite?Answer: Its Mohs hardness is between 4 and 5.
Why is the Mohs scale described as ordinal?Answer: Its numbers show the order of scratch resistance, but the intervals between numbers are not equal.
Why can assigning one Mohs hardness value to granite be misleading?Answer: Granite is a rock made of minerals that can have different hardness values.
Which statement best describes an appropriate use and limitation of the Mohs scale?Answer: It can help geologists roughly identify minerals, but it does not precisely predict industrial durability.
Based on the Wikipedia article Mohs scale, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.