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Streak Test identification and geology

The streak test determines the color of a mineral's powder by rubbing it across an unglazed porcelain plate streak plate . While the external color of a mineral can vary widely due to trace impurities, inclusions, or surface weathering, the streak color is far more consistent and diagnostic. For example, hematite may appear silver-gray, red, or brown in hand specimen but always produces a characteristic reddish-brown streak. Streak is especially useful for identifying metallic and dark-colored minerals, where hand-specimen color alone can be misleading. The test works because crushing the mineral into fine powder eliminates the effects of crystal structure on light absorption and reduces the influence of surface impurities. The resulting powder color reflects the mineral's fundamental light-absorption properties. The standard streak plate has a hardness of approximately 6.5–7 unglazed porcelain , so minerals harder than this will not produce a streak—they will instead scratch the plate. For these harder minerals, the streak test is not applicable, and other diagnostic properties must be used. Softer minerals below 2 may leave a streak too faint to read reliably; in such cases, crushing a small fragment with a hammer and observing the powder color on white paper is an alternative. Tips: Do not streak, grind, or scratch an unknown specimen that may be fibrous, radioactive, or contain arsenic, mercury, lead, or other hazardous elements. Avoid creating or inhaling dust. Always use a fresh area of the plate for each test. Ensure adequate lighting—fluorescent lights can distort color perception. Weathered surfaces may give misleading streaks; break the specimen to expose a fresh surface first. For rare or small specimens, minimize material loss by using the shortest possible stroke. A drop of water on the streak can sometimes intensify the color for easier reading.. Equipment: Unglazed porcelain streak plate white , hand lens 10× . Optional: black streak plate for light-colored minerals, small hammer and white paper for very soft or very hard specimens. Procedure: 1. Obtain a clean, dry, unglazed white porcelain streak plate. 2. Select a corner or edge of the mineral specimen. 3. Firmly drag the mineral across the plate in a short stroke 2–3 cm , applying moderate pressure. 4. Examine the resulting powder line on the plate. Note the color under good lighting condi

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-08-27T06:43:51.86382+00:00
Review status
Published; not independently peer-reviewed
  • How Do Geologists Identify Minerals? — Utah Geological Survey. Practical guidance on diagnostic physical properties and identification tests.
  • Mineral ID Key — Mineralogical Society of America. Detailed test methods, repeatability guidance, and safety cautions.

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Common questions

What is the Streak Test used for?
The streak test determines the color of a mineral's powder by rubbing it across an unglazed porcelain plate streak plate . While the external color of a mineral can vary widely due to trace impurities, inclusions, or surface weathering, the streak color is far more consistent and diagnostic. For example, hematite may appear silver-gray, red, or brown in hand specimen but always produces a characteristic reddish-brown streak. Streak is especially useful for identifying metallic and dark-colored minerals, where hand-specimen color alone can be misleading. The test works because crushing the mineral into fine powder eliminates the effects of crystal structure on light absorption and reduces the influence of surface impurities. The resulting powder color reflects the mineral's fundamental light-absorption properties. The standard streak plate has a hardness of approximately 6.5–7 unglazed porcelain , so minerals harder than this will not produce a streak—they will instead scratch the plate. For these harder minerals, the streak test is not applicable, and other diagnostic properties must be used. Softer minerals below 2 may leave a streak too faint to read reliably; in such cases, crushing a small fragment with a hammer and observing the powder color on white paper is an alternative.
How do you perform the Streak Test?
1. Obtain a clean, dry, unglazed white porcelain streak plate. 2. Select a corner or edge of the mineral specimen. 3. Firmly drag the mineral across the plate in a short stroke 2–3 cm , applying moderate pressure. 4. Examine the resulting powder line on the plate. Note the color under good lighting conditions—natural daylight or full-spectrum artificial light is ideal. 5. If no streak appears, the mineral is likely harder than the plate. Record as "no streak" or "white/colorless" if applicable. 6. For light-colored minerals that appear white on a white plate, repeat using a black streak plate to improve contrast. 7. Wipe the plate clean between tests to prevent color contamination. 8. Compare the observed streak color to reference charts or diagnostic tables.
How do you interpret the Streak Test?
Streak color is recorded using standard descriptive terms: reddish-brown hematite , yellow-brown limonite/goethite , black magnetite, pyrolusite , greenish-black chromite , pale blue azurite when powdered , white/colorless most silicates and light-colored minerals . The key diagnostic value lies in cases where streak differs markedly from hand-specimen color. If the mineral scratches the plate without leaving powder, its hardness exceeds 6.5 and other identification methods should be used.
What equipment is needed for the Streak Test?
Unglazed porcelain streak plate white , hand lens 10× . Optional: black streak plate for light-colored minerals, small hammer and white paper for very soft or very hard specimens
What safety precautions apply to the Streak Test?
The listed safety level is caution.

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