Question

What physical property can be shown by scratching one material with another?

Answer 1

You speak of Friedrich Moh's scale of mineral hardness.

Explanation:

As the article relates, the relative hardness of minerals had been considered since antiquity. Moh arbitrarily placed talc at no. 1 on the scale, i.e. the least hard mineral, and at 9, and 10, the hardest minerals, carborundum, and diamond. The scale is non-linear, but probably highly useful for a geologist.