Minerals: Streak

To perform the streak test, you rub a specimen on a piece of unglazed porcelain tile. Go to your local hardware store, and look at the backs of their floor tiles. You want a tile that is made of porcelain, and the unglazed back should have a white color.

These tiles are very hard (hardness 6.5), and they have a rough surface. As you rub the mineral across that surface, it acts like a file, powdering up some of the mineral. The color of that powdered mineral is its streak color.