The average dry surface hardness (Rockwell hardness) of the Type IV stone is
The avenge dry surface hardness of the Type IV stones is approximately 92 (Rockwell hardness) and that of Type III stone is 82. Even though the surface of the Type IV stone is harder, care should be taken when the pattern is being carved.
Phillips Science of Dental Materials ed 12 pg 191
92
82
72
65