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Mineral Streak

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A mineral's streak is the color it has when ground to a powder. Some minerals that occur in a range of colors always have the same streak, thus streak is considered a more stable indicator. The great majority of minerals have a white streak, but there are a few well-known minerals for which the streak is an important property.

The simplest way to make a powder is to grind the mineral on a small rectangular piece of unglazed ceramic called a streak plate. Streak plates have a Mohs hardness around 7, but be sure to check your streak plate against a piece of quartz (hardness 7) because some are softer and some harder. The streak plates shown here have a hardness of 7.5. An old kitchen tile or even a sidewalk can also serve as a streak plate. Mineral streaks can usually be wiped off easily with a fingertip.

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Two kindsStreak PlatesNot diagnostic of muchThe Typical White StreakBe sure to checkBeware of ScratchesBlack plates pay offIdentifying Native Metals by Streak
Two special streaksCinnabar and Hematite StreaksTelltale streakIdentifying Galena by StreakBlack streakIdentifying Magnetite by StreakNot for differentiationStreak of Copper Sulfide Minerals
Streak is often definitiveGoethite and Hematite Streaks
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