Pyrite or Iron Pyrite (FeS2) is a very common mineral that is present in many sedimentary rocks as framboidal crystals. Subject to certain conditions, pyrite is problematic in confined construction, such as under floor filling and bridge embankments. This is due to a chemical reaction that can cause pyritic backfill to swell.

Construction material containing relatively large amounts of pyrite minerals are likely to expand, crack and/or crumble over time. This occurs when framboidal crystalline pyrite, air and moisture, mix causing a chemical reaction to occur that creates expanding crystals within the material.

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