Near Syracuse, New York. In roughly the same length of time, this marble headstone has weathered appreciably. Lettering is rounded, the surface is rough, and the stone is stained by organic acids. 2500 years of exposure to salt air will do this to marble. A wall at Cape Sounion, Greece.
Rocks weather at different rates.
The dark gray rock, rich in ferromagnesian minerals, is so crumbly it can be dug by hand. The dikes and sills, mostly quartz and feldspar, are much less weathered. San Bernardino Mountains, California. 400 years of pedestrian traffic has differentially eroded this marble floor in St. Peter's, in Rome. A century of foot traffic in the State Capitol, in Madison, has resulted in noticeable differential wear.