Streak
Streaks are the color of a mineral when it is flaked by scratching it on an unfrozen surface. Unlike apparent color, which is easily changed by the form and internal composition of minerals, it has a certain color, so it is useful for distinguishing similar minerals with similar color. For example, ruby and sapphire are aluminum oxide crystals in which iron, titanium, or chromium are mixed in a minute amount, and appear strikingly different colors due to changes in composition of internal metal elements, but streaks are the same. On the other hand, natural gold, pyrite and chalcopyrite are similar in color, but streaks are different in yellow, green and rust black.