Pyrite and pyrrhotite

Pyrite is an iron sulphide molecule present in the backfill stone used in construction. It can therefore be found around foundation drains and under basement or garage slabs.

Under certain conditions, pyrite can oxidize and produce a white powder that can swell and cause problems such as buckling of the slab and cracks in foundations and walls. These problems can appear several years after construction.

Pyrrhotite, on the other hand, is a mineral composed of iron sulphide. It is bronze yellow in colour and turns black when exposed to air. By crystallizing into strips, it can cause cracks in concrete.

Problems related to pyrite and pyrrhotite have been and continue to be observed in certain regions of Québec

For more details: High-risk areas for pyrite: Broker responsibilities