For many years the estimation of the hardness of minerals has been based on the relative hardness of the minerals comprising the Mohs scale. It has been impossible to make hardness measurements with the Brinell or Rockwell tester on mineralogical samples because of the great forces involved, resulting in shattered crystals. In general, many other hardness testing methods are subject to this condition in a greater or lesser degree. It is true that obtaining an estimation of the hardness of the minerals in the Mohs scale, using one of the standard hardness testers, is mainly of academic interest. However, since this scale has had such widespread use and since the studies3 of the hardness increments between adjacent steps have given, for the most part, discordant results, we have believed it pertinent to undertake a preliminary study, using the microcharacter,4 a standard hardness tester designed for work on bearing metals.

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