USGS Releases Map on Pyrrhotite

Pyrrhotite is an unstable form of iron sulfide mineral in geologic formations. Its presence in aggregate from one quarry in Connecticut has been attributed to extensive cracking in several residential foundations in Connecticut and Massachusetts. In connection with these developments, the U.S. Geological Survey (USGS) issued this press release. The USGS has released its first-ever map of where the mineral pyrrhotite may occur in the contiguous United States. This research was mandated by Congress in the FY2019 appropriations bill for the USGS and was supported by the USGS Mineral Resources Program.

Pyrrhotite, a mineral of concern for the construction industry, consists of iron and sulfur. When exposed to water and air, it can break down to form secondary minerals that expand and crack concrete, causing concrete structures, like home foundations, to fail. “This project was a bit unusual for us, because typically we’re trying to help people find mineral deposits that they want, not minerals that they don’t want,” said USGS scientist Jeff Mauk, who led the project. “Pyrrhotite in concrete has caused enormous problems for homeowners in parts of Connecticut and Massachusetts.”

The map identifies locations where the mineral may potentially occur, but has not been confirmed. However, the map could be interpreted as a location of potential problem areas for aggregate sources. The location of this mineral has been identified in the quarry in Connecticut and to two in the Quebec province of Canada. The Concrete Foundations Association published an information sheet in 2016 with input from knowledgeable researchers. ACI Committee 201 is completing a tech note on pyrrhotite and mechanism of deterioration it causes in concrete. The USGS fact sheet and other documents are available here.