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In a laboratory, you scratch an unknown mineral on a piece of unglazed porcelain. We are trying to determine streak. So, the correct option is (c).
When a mineral is dragged across an unweathered surface, powder is formed that is the colour of the mineral's streak. The trail of finely ground powder typically has a more consistent characteristic colour than the apparent colour of a mineral, which for most minerals can vary significantly. This makes the trail of powder an important diagnostic tool in the identification of minerals.
The mineral's streak is described as being white or colourless if it doesn't appear to be making any. For opaque and colourful materials, streak is particularly crucial as a diagnostic. For silicate minerals, which typically have a white streak or are too hard to powder easily, it is less effective.
Learn more about mineral's streak here;
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