# Mineral streak test

Canonical page: https://lithomap.app/resources/field-tests/mineral-streak-test
Last reviewed: September 18, 2026
Page purpose: Original LithoMap field-method reference for human readers, search systems, and language models.

## Direct answer

Draw a clean, unweathered corner across unglazed porcelain with moderate pressure, then observe the powder color in neutral light. A specimen harder than the plate may scratch it without producing a useful streak.

## Why the test works

Surface color can change with tarnish, staining, inclusions, or weathering. Powdering many tiny grains reduces some of those surface effects.

Streak is most diagnostic for minerals that yield a colored powder. Many pale nonmetallic minerals produce a white or nearly colorless streak, so the result must be combined with other evidence.

## Field kit

- White unglazed porcelain streak plate
- Optional black streak plate for very pale powder
- Clean specimen corner
- Hand lens
- Soft brush or damp cloth for cleanup

## Procedure

1. Choose a clean point: Use an unweathered edge that represents the mineral of interest, not the surrounding rock, rust coating, or soil.
2. Make one short pass: Pull the specimen across the rough porcelain for about one to two centimeters with moderate pressure.
3. Separate powder from a scratch: Colored powder is a streak. A gouge with little powder means the specimen may be harder than the plate.
4. View in neutral light: Describe the powder precisely—red-brown, yellow-brown, gray-black, green-black, white—rather than copying the specimen’s body color.
5. Confirm and clean: Repeat on a fresh spot if the first line crossed a coating or mixed grain. Clean reusable plates so old residue does not contaminate the next test.

## Interpreting results

- Red to reddish-brown powder: Strong evidence for hematite or hematite-rich material, even when the specimen looks steel gray or black.
- Yellow-brown to brown powder: Consistent with goethite and some hydrated iron-oxide mixtures.
- Black powder with strong magnetism: Supports magnetite, but mixtures and other dark magnetic minerals require additional checks.
- White or nearly colorless powder: Common among many nonmetallic minerals and rarely diagnostic by itself.
- Plate is scratched with little powder: The specimen is likely harder than the plate; record the streak as unavailable rather than guessing.

## Examples and related guides

- Hematite: Red-brown streak despite highly variable surface appearance. — https://lithomap.app/resources/mineral-identification/hematite
- Goethite: Usually yellow-brown to brown streak. — https://lithomap.app/resources/mineral-identification/goethite
- Magnetite: Black streak paired with strong magnetic response. — https://lithomap.app/resources/mineral-identification/magnetite
- Pyrite: Dark greenish-black to brownish-black streak, not gold colored. — https://lithomap.app/resources/mineral-identification/pyrite

## Common mistakes

- Testing a rusty coating instead of the underlying mineral
- Calling a porcelain scratch a streak
- Using glazed tile, which lacks the required abrasive surface
- Letting residue from an earlier sample alter the color
- Assuming a white streak identifies a single mineral

## Safety and limitations

- Use minimal pressure and avoid breathing powder.
- Do not streak fibrous material, lead-bearing material, radioactive candidates, or unknown mine waste.
- Wash hands after testing and keep plates away from food-preparation surfaces.
- Only test material you may lawfully possess and alter.

## Frequently asked questions

### Why is streak sometimes more useful than color?

Tarnish, staining, and trace impurities can change a specimen’s surface color. Powder color is often more stable, although it is not unique for every mineral.

### Why did my specimen scratch the streak plate?

Unglazed porcelain is commonly around Mohs 6.5 to 7. A harder specimen may cut the plate instead of leaving enough powder for a meaningful streak.

### Can I use the unglazed ring under a mug?

It may work for a rough check, but ceramics differ and the object can be damaged. A purpose-made clean streak plate is safer and more consistent.

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Geology Lesson 2: Global Building Blocks — U.S. National Park Service: https://www.nps.gov/teachers/classrooms/geology-lesson-2-global-building-blocks.htm
- Kansas Rocks and Minerals: Mineral Identification — Kansas Geological Survey: https://www.kgs.ku.edu/Publications/Bulletins/ED2/07_ident.html

This method supports preliminary field identification. It is not laboratory confirmation, appraisal, hazard clearance, proof of origin, or permission to collect or alter a specimen.