Final answer:
You are checking for the physical property known as streak when you scrape a mineral along a ceramic plate to observe its powder color, which differs from its actual color, particularly in metallic minerals.
Step-by-step explanation:
When you scrape a mineral along a ceramic plate to observe the color of its powder, you are checking the physical property known as streak. Streak describes the color of a mineral in powdered form which can be different from the color of the mineral itself. This is because the powder form minimizes the effect of impurities that can affect light absorption and hence the perceived color. Streak is particularly useful for identifying metallic minerals as these tend to have a different streak color than their actual appearance, whereas non-metallic minerals often have a white streak or a streak color similar to the mineral itself. Cleavage refers to the way a mineral breaks along certain planes and is signified by flat surfaces, which can be seen by how the light reflects off the mineral's surface. Luster is the way a mineral reflects light which can be metallic or non-metallic, with metallic luster being those that do not allow light to pass through, unlike non-metallic luster.