The mineral property identified by the color of powder left behind when it rubbed across a surface is called streak. Streak is the color of the mineral in its powdered form and it is different from the color of the mineral in its massive form. Streak is an important diagnostic property used in mineral identification as it can help to distinguish between minerals that have similar colors. For example, pyrite and chalcopyrite are both brassy yellow in color but pyrite has a black streak while chalcopyrite has a greenish-black streak.