It is important to note that color alone is not an indication of the physical qualities of the stone. In general, granite’s color is directly related to the presence or absence of minerals, which may have no bearing on the qualities that make good surface plate material. There are pink, gray, and black granites that are excellent for surface plates, as well as pink, gray, and black granites that are totally unsuitable for precision applications. The critical characteristics of granite, as they pertain to its use as a surface plate material, have nothing to do with color, and are as follows:
Stiffness (deflection under load – indicated by Modulus of Elasticity)
Hardness
Density
Wear resistance
Stability
Porosity