Streak The color of the mineral in powdered form, called streak, is often useful in identification. A mineral's streak is obtained by rubbing it across a streak plate(a piece of unglazed porcelain) and observing the color the mark it leaves of(Figure 2.12). Although the color of a mineral may vary from sample to sample, its streak is usually consistent in color.
Streak can also help distinguish between minerals with metallic luster and those with nonmetallic luster. Metallic minerals generally have a dense, dark streak, whereas minerals with nonmetallic luster typically have a light-colored streak.
It should be noted that not all minerals produce a streak when rubbed across streak plate. For example, the mineral quartz is a harder than a porcelain streak plate. Therefore, no streak is observed using this method.