Pyrite is a mineral contained in several rock formations. When in contact with moisture and oxygen, pyrite swells.
The pyrite problem affects constructions that use a fill containing pyrite under the foundation slab of basements and garages. With time, pyrite inflates and lifts the concrete slab and foundation walls.
In Quebec, the pyrite problem is endemic to the Montérégie region, in the south of the metropolitan area and around the St. Lawrence Valley. Buildings constructed in 1980 are particularly likely to experience this problem.