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Refreshing Your Streak Plate
Streak plates that have been used heavily will be covered with streaks and powdered mineral. They can easily be cleaned with water and a piece of wet or dry 220 grit sandpaper. Aluminum oxide or silicon carbide sandpaper works best because the granules are hard enough to smooth the surface of the streak plate. The…
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Don’t Be Deceived!
A number of things can cause a streak test to give unreliable results. To avoid problems, keep the following items in mind.
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Why Use the Streak Test?
The streak test is valuable because many minerals occur in a variety of apparent colors – but all specimens of that mineral share a similar streak color. For example: specimens of hematite can be black, red, brown, or silver in color and occur in a wide variety of habits; however, all specimens of hematite produce a streak with…
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Don’t Be Wimpy!
The most common error made by people who are doing the streak test for the first time is to lightly rub the specimen back and forth on the surface of the streak plate. This will not produce a proper streak. Some mineral specimens are so hard that very firm pressure and determination are required to…
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How to Conduct the Streak Test
The streak test should be done on clean, unweathered, or freshly broken specimens of the mineral. This is done to reduce the possibility that a contaminant, weathered coating, or tarnish will influence the results of the test. The preferred method for conducting a streak test is to pick up a representative specimen of the mineral…
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What is the Streak Test?
The “streak test” is a method used to determine the color of a mineral in powdered form. The color of a mineral’s powder is often a very important property for identifying the mineral. The streak test is done by scraping a specimen of the mineral across a piece of unglazed porcelain known as a “streak plate.” This…
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The Complex Work of Meteorologists
Meteorologists have a challenging job. If they forecast snow, they need to determine when a moisture-laden air mass will pass over an area and if the temperature high at the snowflake-forming elevation will be below freezing. They also need to determine if the temperatures at lower elevations will allow the snowflake to fall to the…
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Freezing Rain
If the snowflakes pass through a layer of warm air that is thick enough to melt them completely, then land on a cold Earth surface, the result could be freezing rain.
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Sleet!
If the snowflakes pass through a thin warm layer of air, they could experience partial melting. When they exit the warm air, they will refreeze on the way down in the form of a tiny ice pellet. This is how sleet forms.
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Will They Reach the Ground as Snow?
The formation of snowflakes high in Earth’s atmosphere does not guarantee snowfall on Earth’s surface. That will only happen if air temperatures are below freezing all the way to the ground, as shown in the accompanying illustration.