Streak
- The streak is the powdered form of the mineral.
- When a mineral is rubbed against unglazed porcelain tile it leaves a streak.
- Porcelain tile has a hardness value of 7.
- Minerals that have a hardness value of more than 7 don't leave a streak.
- Graphite is the mineral used in pencils.
- Pencil marks are graphite streaks that are soft enough to be left on a piece of paper.
- A streak test is one way to identify whether a mineral sample is gold or pyrite. Gold leaves a golden
streak. Pyrite leaves a greenish-black or brownish black streak.