the color of the minerals. which minerals scratch other minerals. which minerals reflect light most strongly. the samples that feel smoothest to the touch.
I gave my students this multiple choice question: To compare the hardness of different minerals, it would be BEST to find

Only one answer is correct among these 4 choices:
- the color of the minerals.
- which minerals scratch other minerals.
- which minerals reflect light most strongly.
- the samples that feel smoothest to the touch.

Could you tell me which one is correct?

which minerals scratch other minerals.