Massachusetts Hornfels-Braintree Slate Quarry

The Massachusetts Hornfels-Braintree Slate Quarry is a prehistoric archaeological site in Milton and Quincy, Massachusetts. It consists of a series of pits and trenches used from 5,000 B.C. until the early 17th century as a source of slate and hornfels used for chipped and ground tools. Pieces made from material quarried at the site are found over much of eastern Massachusetts. The site was added to the National Register of Historic Places in 1980.

Archaeological site data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).