What is the streak test?
The streak test means rubbing a rock across an unglazed white ceramic tile to see the colour of its powder. Most meteorites leave little or only a faint grey streak, so a strong red-brown or black streak points to Earth minerals such as hematite or magnetite.
Many minerals reveal their identity not by the colour of the lump, which can vary, but by the colour of their powder, called the streak. Geologists make a streak by scraping the mineral across a streak plate, a piece of unglazed white porcelain. The back of an ordinary bathroom tile, where there is no glaze, works well.
For meteorite hunters, the test is mainly a way of ruling things out. Two of the commonest meteorwrongs are iron ores. Hematite leaves a distinctive reddish-brown streak, a bit like dried blood, even when the lump itself is grey or black. Magnetite leaves a black or very dark grey streak. Both minerals are heavy, and magnetite is strongly magnetic, so they often get mistaken for meteorites.
Most stony meteorites, by contrast, leave little streak or only a faint grey one. Be aware that weathering complicates this. A meteorite that has lain in the ground for a long time may have a rusty coating that leaves a brownish mark. That is why a streak is a clue, not a final answer.
To try it, choose an inconspicuous corner and rub firmly with a short stroke, then wipe away any loose grains and look at the colour left on the tile. Don't scrape away a large area: if the stone does turn out to be a meteorite, its crust is valuable to scientists. The streak test is safe for children with an adult nearby, unlike tests involving acid or heat, which nobody should use on a suspected meteorite. A positive identification still needs an expert.