Final answer:
A diamond does not leave a streak on a streak plate because it is too hard, scoring a 10 on the Mohs hardness scale, and would instead damage the streak plate.
Step-by-step explanation:
A diamond will not leave a streak on a streak plate. Streak testing is a method used in mineralogy to help identify minerals based on the color of the streak they leave behind when dragged across a piece of unglazed porcelain, known as a streak plate. The streak of a mineral is essentially the color of its powder form. Because diamonds are incredibly hard, ranking at a 10 on the Mohs scale of mineral hardness, they do not powder when scratched against a surface but rather might scratch or damage the streak plate itself.