Colour can vary within one mineral, so it may be a weak identifier. Streak can be more consistent, and lustre adds another observation. Use the candidate table, then choose a test. If a specimen scratches calcite but is scratched by quartz, its hardness lies between those references.
Earth and geology · Discover & try
How can tests distinguish minerals?
Reading level 3 of 5 · IndependentChange
Word help
Hardness
Relative resistance to scratching.
Streak
The colour of a mineral’s powder on a streak plate.
Lustre
How a mineral surface reflects light.
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See how it works
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Virtual tests and reference properties; original crystal drawings are not measured specimens or a complete identification key.
What to look for
- Use a harder and a softer reference.
- Compare the remaining candidate set.
- Do not treat the Mohs scale as a linear ratio.
Explain what you noticed
An unfamiliar specimen scratches calcite (3) but is scratched by orthoclase (6). What is supported?
Keep this idea: Several properties are more useful than colour alone, and hardness describes scratching resistance.
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