Sapstone rust

The orange-brown granite across the quarry to your left is called seam-faced granite. It was colored over many thousands of years as water seeped through the naturally- occuring cracks in the granite, causing the iron-containing minerals in the granite to oxidize or ‘rust’. During the 19th century, this sapstone was considered undesirable because of its color, but after 1900 it came into fashion as veneer for the surfaces of buildings. After being removed from the quarry, it was taken to a cutting shed, cut into pieces several inches thick, and polished to a high gloss.

definition from the:
Halibut Point State Park, Massachusetts Department of Conservation and Recreation brochure – 1999
Babson Farm Quarry Self-guided Walking Tour