Intro
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Streak is the color of a mineral in powdered form. It is determined by rubbing a mineral across an unglazed porcelain surface. Streak is often more reliable than surface color when identifying minerals.
• Shows the true powdered color
• More consistent than surface appearance
• Helpful for identifying metallic minerals
How to Perform a Streak Test
A streak test is simple and requires a streak plate.
• Use unglazed porcelain
• Rub the mineral firmly across the surface
• Observe the color of the powder left behind
The streak color may differ from the mineral’s visible color.
Why Streak Is Useful
Surface color can vary due to impurities or weathering.
Streak helps because:
• It shows a consistent color
• It reveals hidden mineral characteristics
• It helps distinguish similar-looking minerals
This is especially helpful with metallic minerals.
Examples of Streak Differences
Some minerals look similar but have different streak colors.
• Hematite may appear silver but has a reddish-brown streak
• Pyrite has a greenish-black streak
• Magnetite leaves a black streak
Streak often confirms identification.
When Not to Use a Streak Test
Some minerals are too hard or too valuable to test.
• Very hard minerals may scratch the plate
• Rare or delicate specimens should not be tested
In those cases, use other identification methods.
Why Streak Matters for Beginners
Streak helps beginners:
• Avoid relying only on surface color
• Improve identification accuracy
• Learn consistent testing methods
It is a foundational mineral property.
Conclusion
Streak reveals the true powdered color of a mineral and is a reliable identification tool. When used carefully, it helps distinguish between similar-looking specimens.
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