Mineral Streak

Problem

What is streak and how can it be used to identify a mineral?

Materials

• Piece of unglazed white porcelain (back of tile would work fine)
• Assorted metallic and non-metallic minerals. good choices include:
  • Iron pyrite
  • Hematite
  • Mica
  • Talc
  • Halite
  • Magnetite

Procedure

1. Make a table similar to the following

2. Record the color of the mineral sample in your data table.
3. Rub the mineral sample across the streak plate. Record the color of the powder on the plate. If your mineral sample is very hard, the powder you see might be that of the streak plate rather than the mineral itself.

Results

Minerals that contain metals tend to make a streak at least as dark as the mineral itself, while nonmetallic minerals tend to make clear or white streaks. Iron pyrite makes a greenish-black streak, while hematite makes a reddish-brown one. Talc, mica, and halite all make white streaks.

Why?

Minerals are made of elements, or compounds that have distinctive properties. Some of the most valuable minerals contain metals. Metals, like gold, iron, copper, and silver are easily shaped. Many can be used for cooking and carrying electricity. In their pure form, metals often appear shiny. Powdered metals often appear dark. Iron pyrite and hematite both contain metals; talc, mica and halite do not.

Going Further

There are many other tests you can do to identify minerals. Since both gold and iron pyrite contain metals, streak alone can’t help you tell a gold nugget from a pyrite nugget—but measuring density can. Find the volume and mass of your sample. Divide the mass by the volume. Pure gold has a density of 19 g/mL, while Iron pyrite has a density of 5 g/mL.