Streak (mineralogy)

However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, and small impurities do not greatly affect the absorption of light.

In the absence of a streak plate, the unglazed underside of a porcelain bowl or vase or the back of a glazed tile will work.

For harder minerals, the color of the powder can be determined by filing or crushing a small sample, which is then usually rubbed on a streak plate.

Other minerals leave surprising colors, such as fluorite, which always has a white streak, although it can appear in purple, blue, yellow, or green crystals.

Hematite, which is black in appearance, leaves a red streak which accounts for its name, which comes from the Greek word "haima", meaning "blood."