We all know that hard materials scratch soft materials, and the effectiveness is related to the difference in their Moh's hardness level. My question is whether some minute amount of abrasion occurs on the harder material that is scratching the soft material? If so, is there any mathematical relationship to the amount of abrasion to the soft material? (I am thinking of it might be inversely related to the difference in Moh hardness, then probably raised to an exponent.) My curiosity came about as I recently bought a stylus for my smartphone. The stylus (Retrak) is not rubber tipped, instead it has a cloth tip which is impregnated with nano-sized silver particles. Silver has Moh's hardness of 3, whereas the smartphone has glass with hardness of 7. So, the stylus is softer than the glass, but could abrasion to the glass still arise over repeated use?