Ask-a-Geologist Q&A Video #12: How do you clean streak plates?

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How do you clean streak plates that are dirty from testing minerals?

Our readers have some amazing questions and this one is no exception. In fact, this is a very popular question that people send us about how to clean streak plates that you use to test mineral samples.

How do I Clean Streak Plates after Testing Minerals?

In case you are not familiar with streak plates, they are little pieces of unglazed porcelain tile that you use to test the streak color of a mineral. There are black streak plates and white streak plates. You use the black plates for light-colored minerals and white plates for dark-colored minerals.

White Streak Plates for Mineral Testing

How to Test Mineral Streak

To test the streak, you rub the mineral across the streak plate and see what color shows up on the plate. That is the streak or the color of the mineral in powdered form. When you do the test you need to rub hard on the streak plate because you are trying to crush part of the sample into a fine powder. Over time the plates will become dirty and you will want to clean them.

Methods for Cleaning Streak Plates After Use

There are a couple of things that you can do to clean the streak plates. For some of them, you can soak them in warm soapy water for a few minutes then use a kitchen sponge to scrub the surface. This works pretty well to remove the powder of some of the softer minerals. Now a streak plate is about a seven on the Mohs Hardness scale so any mineral that is a seven or higher on the scale will not show a streak because they are harder than the plate. However, these harder minerals will scratch the surface of the plate making them harder to clean because the mineral powder gets ground into the porcelain.

For plates that are older and scratched you can use this handy scrubber called the Magic Eraser. These are made by Mr. Clean and you just get them wet and then rub them over the streak plate and they come clean. Over time the plates will get scratched and stained to the point where even the magic eraser won’t work and you will need to replace them but routinely cleaning your streak plates will help keep them nice for many uses.

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