Starrett Granite Surface Plates:

The granite for Starrett surface plates has been selected for the best balance of physical properties, maximum resistance to wear and for deflection under load. Each plate has been lapped to a fine micro inch finish to minimize tool wear and drag.

The most important element in the performance and life of granite surface plates is the percentage of quartz that is present in the stone. Quartz is more than twice as resistant to wear as the other minerals in granite. It provides bearing points that are of a hard, highly polished, smooth character which protect the accuracy and finish of both the surface plate and the tools and instruments used on it.

Starrett Crystal Pink Granite has the highest percentage of quartz of any granite. Higher quartz content means greater wear resistance and thus greater value. The longer a surface plate holds its accuracy, the less re lapping has to be done.*

*Text from "576ÊStarrett" .pdf at starrett.com