When a mineral is rubbed against a piece of porcelain tile,
a streak of powered mineral remains on the tile. This streak can be an
important clue because the color may vary from the color seen on the surface
of the specimen. Streak is especially useful in identifying metallic minerals
because they tend to tarnish or rust during the weathering process. By
using the streak test, you will be able to determine the mineral's true
color.
This light colored mineral leaves a dark colored
streak.
This dark colored mineral leaves a light colored
streak.
