How to do a streak test at home (and what the color means)

By the Little Finders Club team · 18 October 2026

The short answer

Rub a mineral firmly across unglazed white porcelain, such as the back of a bathroom tile, and look at the color of the powder line. The streak color is often a better clue than surface color: hematite leaves reddish brown, pyrite greenish black, and gold yellow.

A streak test shows the color of a mineral's powder, which is often a better clue than the color of the rock itself. All you need is a piece of unglazed white porcelain and a minute of time. Here is how to do it, what the color tells you, and a few other easy tests to try at home.

What you need

A streak plate. This is just unglazed white porcelain. Rock shops and science kits sell them cheaply, but the rough, unglazed back of a white bathroom or kitchen tile works too. The shiny glazed side will not work.
Your mineral. A piece with a clean corner or edge is best.
A damp cloth to wipe the plate between tests.

How to do a streak test

Lay the tile flat on a table so it cannot slide.
Choose a fresh corner of the mineral, not a dusty or weathered surface.
Press firmly and drag the mineral across the tile in one short line, like drawing with chalk.
Gently blow away loose grit and look at the color of the powder line.
Compare it with the color of the outside of the mineral, then wipe the tile clean.

Why streak color beats surface color

A mineral's outside color can change because of tiny impurities, weathering, or a thin coating. Fluorite, for example, can be purple, green, yellow, blue, or clear. Its powder, though, is white every time. Because the streak stays much more consistent, it is one of the best clues for telling look-alikes apart.

Mineral	Surface color	Streak color
Hematite	Silvery gray, black, or rusty red	Reddish brown
Pyrite ("fool's gold")	Brassy gold	Greenish black to brownish black
Gold	Gold yellow	Yellow
Magnetite	Black	Black
Fluorite	Purple, green, yellow, blue, or clear	White

The pyrite and gold pair is the classic example. They can look almost the same, but pyrite's dark streak gives it away.

When there is no streak

A streak plate is about 6.5 on the Mohs hardness scale, which runs from 1 (very soft) to 10 (diamond). Minerals harder than the plate, such as quartz, topaz, and corundum, will not leave a powder line. Instead they may scratch the tile and leave a little white porcelain dust. If that happens, the useful result is "harder than the plate," not "white streak."

Other easy tests at home

Scratch test (hardness)

Try to scratch the mineral with these, from softest to hardest:

Fingernail (about 2.5). If your nail scratches it, it is very soft, like talc or gypsum.
Copper (about 3). An old copper penny or a bit of copper wire works. Calcite is about this hard.
Steel nail (about 5.5). Many common minerals scratch with steel. Quartz does not.
Glass (about 5.5). Turn it around: can the mineral scratch glass? Quartz scratches glass easily.

Rub the mark with your thumb afterward. A real scratch stays. A powdery line that wipes away is just a streak left by the softer object.

Magnet test

Magnetite sticks strongly to a magnet. A few other minerals are weakly magnetic, and most are not magnetic at all. A strong fridge magnet on a string makes small pulls easier to notice.

Vinegar fizz test

Put a few drops of vinegar on the mineral. Calcite, and rocks made of it like limestone and marble, slowly give off tiny bubbles. Vinegar is a weak acid, so the fizz is gentle. Scraping a little powder first, or using slightly warm vinegar, makes it easier to see. Rinse the rock afterward.

When two minerals look alike, Rockbud's Confirm-it test suggests which one of these checks will tell them apart.

Safety: Never lick or taste minerals. Some contain harmful elements like lead or arsenic, so wash your hands after handling rocks. Wear eye protection when scratching or chipping, and let an adult handle glass and sharp tools.

Quick answers

What can I use instead of a streak plate?

The unglazed back of a white ceramic tile works well. It needs to be rough, unglazed porcelain. The shiny glazed side is too smooth to rub off any powder.

Why does silver-colored hematite leave a red streak?

A mineral's surface color can look different from its powder, depending on how light reflects off the surface. When hematite is ground into fine powder on the plate, its true reddish-brown color shows, whatever the outside looks like.

Can you do a streak test on quartz?

Not really. Quartz is harder than a streak plate, so it scratches the tile instead of leaving a colored line. A scratch test works better: quartz easily scratches glass, and a steel nail will not scratch it.