Source : Webster's Revised Unabridged Dictionary (1913)

Sclerometer \Scle*rom"e*ter\, n. [Gr. sklhro`s hard + -meter.]
   An instrument for determining with accuracy the degree of
   hardness of a mineral.

Source : WordNet®

sclerometer
     n : a measuring instrument that measures the hardness of
         materials by penetrating them with a stylus that has a
         diamond point