Pyrrhotite Distribution in the Conterminous United States, 2020

Fact Sheet 2020-3017
By: , and 



In parts of Connecticut and Massachusetts, foundations of some homes are cracking and crumbling. Failing foundations can reduce the market value of a home and lifting a house to replace and repour a foundation is an expensive undertaking. In response, some homeowners are defaulting on their mortgages and abandoning their homes. The culprit is pyrrhotite, which occurs in construction aggregate (crushed stone) that was used as a filler in concrete. When pyrrhotite is naturally exposed to water and oxygen, it breaks down to produce sulfuric acid and secondary minerals, including gypsum, which have larger volumes than the pyrrhotite they replace. The expanded volume of the secondary minerals cracks and degrades concrete.

Pyrrhotite occurs in rocks in many areas of the United States. To help assess the national risk of pyrrhotite in aggregate, the fiscal year 2019 appropriations bill for the U.S. Geological Survey’s (USGS) Mineral Resources Program allocated funds to develop a map showing the distribution of pyrrhotite across the United States. The purpose of this fact sheet is to (1) present a nationwide map that shows where pyrrhotite may occur in rocks in the United States, (2) describe and discuss the factors that control the presence and abundance of pyrrhotite in rocks, (3) provide information on geographic information system datasets that deliver more detailed information on these distributions, and (4) describe U.S. and international standards on aggregate that are designed to prevent failing concrete.

While this map and fact sheet provide general information about the possible distribution of pyrrhotite in the United States, they are no substitute for site-specific characterization and quality control programs designed to ensure that aggregate used in concrete is of appropriate quality for its intended purpose.

Suggested Citation

Mauk, J.L., Crafford, T.C., Horton, J.D., San Juan, C.A., and Robinson, G.R., Jr., 2020, Pyrrhotite distribution in the conterminous United States, 2020: U.S. Geological Survey Fact Sheet 2020-3017, 4 p.,

ISSN: 2327-6932 (online)

ISSN: 2327-6916 (print)

Study Area

Table of Contents

  • Introduction
  • Pyrrhotite Formation in Rocks
  • Mapping the Possible Distribution of Pyrrhotite in the Conterminous United States
  • Limitations of the Geologic Map Databases
  • Standards for Construction Aggregate
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Pyrrhotite distribution in the conterminous United States, 2020
Series title Fact Sheet
Series number 2020-3017
DOI 10.3133/fs20203017
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Central Mineral and Environmental Resources Science Center
Description Report: 3 p.; Data Release
Country United States
Other Geospatial Conterminous United States
Online Only (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details