The "streak test" is a method used to determine the color of a mineral in powdered form. The color of a mineral's powder is often a very important property for identifying the mineral.
The streak test is done by scraping a specimen of the mineral across a piece of unglazed porcelain known as a "streak/scratch plate." This can produce a small amount of powdered mineral on the surface of the plate. The powder color of that mineral known as its "streak."