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How to Do a Streak Test With Rocks

One way geologists identify minerals is through a streak test. A mineral̵7;s streak is the color it leaves behind on an unglazed piece of white porcelain or ceramic tile -- the color that shows is actually the mineral̵7;s crushed powder, and it can be a different color than the rock itself. Hematite, for example, might have a red or black color, but it always leaves a red streak, so the streak test is a useful identification tool.

Things You'll Need

Streak plate
Nail
Rocks
Mineral identification chart

Instructions

- 1
  Rub a rock across the back of a streak plate. Don't push too hard or you may damage the plate.
- 2
  If the rock does not leave a streak, but rather an indentation or scratch, the rock is too hard for the streak plate. In this case, scrape a nail across the rock. The nail should shave off some of the mineral̵7;s powder so you can see its color.
- 3
  Observe the color left behind on the streak plate or from the mineral̵7;s powder. Is it the same color as the rock? Some minerals like malachite are no surprise because the green rock leaves a green streak. Other minerals like fool̵7;s gold look brassy as a rock but leave a black streak. Gems like amethyst or tourmaline almost always leave a white or colorless streak.
- 4
  Compare your streak result to an identification chart to determine the rock̵7;s identity.

Rocks & Minerals