A mineral’s streak is its color as a fine powder. That color can differ from the surface you see in your hand: a silver-looking piece of hematite, for example, has a red-brown streak. Brooklyn College’s streak reference shows both appearances side by side.
If you’re learning to identify minerals, streak can help separate lookalikes. The first question is whether a mark really came from the mineral. A hard specimen can scrape white powder from the porcelain plate itself, as the Sternberg Museum of Natural History explains. If you can’t tell where a mark came from, record the result as uncertain.
In this article: surface color and streak · hematite and magnetite · misleading marks · when to skip the test.
Why mineral streak can differ from surface color
Surface color and powder color are separate observations. Impurities can change a mineral’s visible color, while its streak can provide another clue to its identity. The Kansas Geological Survey’s mineral reference describes this distinction.
A conventional streak test uses unglazed porcelain, called a streak plate, to obtain a small trace of mineral powder. It removes material from the specimen, so read when to skip the test before deciding whether it suits your piece.
A useful comparison: hematite and magnetite
Hematite can look black or silver-gray, as well as red or brown. Magnetite is black. Their streak colors help distinguish them when their surfaces look similar.
| Mineral | Surface color | Streak color |
|---|---|---|
| Hematite | Black to silver-gray; earthy forms red to brown | Red-brown to rusty red |
| Magnetite | Black | Black |
Reference properties: University of Minnesota, hematite and magnetite.
Suppose, as a hypothetical example, an instructor reports a red-brown streak from a dark teaching specimen. That supports hematite over magnetite. It doesn’t establish that the whole piece is pure hematite: the university notes that these minerals can occur together. Check whether the other observed properties fit, and keep the identification tentative if they conflict.
If you’re trying to work out whether a magnetic rock is a meteorite, our meteorite guide covers magnetite and hematite as lookalikes and explains how a streak can help rule one out.
When the line on the plate is misleading
A white mark needs a closer look. If the specimen is harder than the plate, it can scratch the porcelain and produce white plate powder. That is not evidence of a white mineral streak. The Sternberg Museum’s streak section explains how this happens.
Use these questions to review an existing result:
- Was mineral powder identified, or was there only a pale line or a groove in the plate?
- Was the tested area an exposed mineral grain, a coating, or an uncertain surface?
- Does the result concern that grain, or has it been applied to the whole rock?
A rock can contain more than one mineral, as the Kansas Geological Survey explains. A result from one part therefore need not describe every part. If you can’t tell whether material came from a coating or the mineral beneath it, leave the streak unresolved; don’t scrape through the coating to settle the question.
If you already have a streak result for a gold-colored grain, use our pyrite and gold comparison to check the reference colors and the limits of that result.
If the attempt produced no identifiable mineral powder, leave the streak unknown. Don’t translate it automatically into “white streak” or press harder to force an answer. Our Mohs hardness article explains the separate question of scratch resistance.
When to leave a specimen untested
Skip streak testing on jewelry, polished keepsakes, coated pieces and valuable specimens. Also leave loose, crumbling or fibrous material undisturbed. For an unfamiliar specimen whose handling requirements you don’t know, ask a geology educator or museum identification service before choosing a physical test.
Mineral specimens vary in fragility and chemical hazards. The Natural History Museum’s account of preparing minerals for display describes why some need specialist handling. A name suggested from appearance alone is not enough to establish that an unknown piece is suitable for abrasion. Don’t grind it, deliberately create loose dust, or blow powder off a test surface.
You can still make progress with clear identification photos and a description of existing surfaces. Send those with the specimen’s known origin and any results already available. “Streak not tested” gives the person helping you an honest starting point.