Streak of Minerals
Streak refers to the color of the powder that is left when a person rubs a mineral across a plate of unglazed white porcelain. Such plates are called "streak plates." The color of a mineral and the color of its streak are not necessarily the same. Pyrite, for example, has a pale brass-yellow color but has a greenish-black streak. In the case of some minerals, the color of the streak is more useful in identifying the mineral than is the color of the mineral itself. Hematite is such a mineral. Its color varies, sometimes red or brown, sometimes steel-gray. But hematite always leaves a unique brownish-red streak. Minerals with a hardness of 7 or higher will not leave a streak. Instead, they scratch the streak plate.