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Mineral Streak is an Important Test to Identify Samples

Geologists use many tests to determine the identity of a mineral such as hardness, color, density, magnetism, luster, and streak. Streak is one of the most important tests that you can perform when you are trying to identify a mineral and especially when you are trying to tell two similar minerals apart.

What is a Mineral Streak?

A mineral’s streak is its color when the mineral in is powdered form.

How do you get a powdered form? The answer lies in these little tools called streak plates.

Streak plates are pieces of unglazed porcelain tile that come in white and black colors and different sizes, typically 1”x2” or 2”x2.”

When geologists use streak plates, they are creating a mineral powder that may or may not be the same color as the mineral. Or the sample may not exhibit a streak at all. Testing the streak color is easy and fun and can be a great experiment for kids of all ages.

How to Perform the Mineral Streak Test

To determine a mineral’s streak color:

  1. Choose a dark streak plate for light-colored minerals and a white streak plate for dark-colored minerals. You can use either color you like but it is easier to tell the streak color if the plate color is opposite of the color of the sample.
  2. Place the plate on a hard surface and scratch the mineral across the plate. The purpose of the test is to break down some of the minerals into a powder on the plate. If you perform the test correctly, you will wear down part of the mineral sample to make sure children understand that is okay and expected.
  3. Observe the color of the powder left on the plate. That color is the streak.

A streak plate has a hardness of about 7 on the Mohs Hardness Scale, which is similar to quartz and amethyst. Minerals with a hardness value similar to and above 7, like corundum and diamond, will not show a streak on the plate and will scratch the porcelain. For minerals that are similar in hardness to the streak plates, you must press the mineral very hard onto the plate to see the color. The harder the mineral, the harder you will likely have to scratch the sample on the plate to see the streak.

Some minerals have a streak color that is the same as their outward color, while others have a different streak color. For example, azurite has a blue outward color, and a blue streak, and limonite is a yellow-brown color both outside and in powder form. Conversely, yellow sulfur has a white streak while gray hematite has a cherry red streak color. The following tables provide some common examples of minerals and their streak color.

For details on how to perform the streak test with your samples and testing plates, you can read this article in the Dig Into Geology of our website.

Caring for Your Streak Plates

Over time, streak plates become dirty. You can clean them by using a warm soapy water mixture and a kitchen sponge. We have a video dedicated to the care of your streak plates, so they are useful tools for years.

Streak Test Experiments are perfect for Kids

Teachers and parents will find that kids love testing mineral samples. With a few cool tools and some free downloadable identification flow charts, you can have hours of fun testing samples and learning about the properties of minerals. Mini Me Geology has an assortment of streak plates that are perfect for classrooms and home use. For additional testing tools, you may like our Rock & Mineral Testing Kit.

If you have questions about using your streak plates to identify your samples, contact us and we will be happy to help you!