Hardness of rocks and minerals
Hardness of rock is generally recognized as an important property of influence on the cutting process and tool replacement rate. The mineralogical composition of rocks is important, because the minerals largely determine the hardness of the rock. Hardness is determined using rebound tests, indentation tests or scratch tests. Rebound tests, such as the Schmidt hammer and Shore scleroscope are well known and commonly used to indicate the unconfined compressive strength of rock. P. J. Tarkoy has developed a method to determine abrasiveness of rock by using the combination of Schmidt hammer rebound and Tabor abrasion test values to predict tunnelling machine performance. In tribological engineering, Vickers-, Knoop-, Brinell- or Rockwell static indentation tests are used to give a measure of hardness of materials. The Rosiwal hardness scale is based on a test which nowadays would be regarded as a measure of the resistance of rock or a mineral against abrasive wear.