When New France’s first settlers discovered deposits of iron pyrite in Quebec, they thought they had hit the jackpot. Unfortunately for them, this "fool's gold" had little value.

Even today, pyrite is sometimes considered a contaminant that can cause various problems, especially when it is present in the fill used in building construction.

But is pyrite-contaminated soil a real danger? Our contaminated soil management experts give you more information.

What is iron pyrite?

Pyrite is an iron sulphide mineral of the sedimentary rock family. It occurs naturally in several types of rock formations, particularly in Quebec and the northeastern United States.

Iron pyrite has a slightly golden colour, a bright metallic luster and it is opaque. It tends to crystallize, so its surface reflects light like gold. Its appearance therefore contributed to early settlers confusing pyrite with real gold. However, around the year 50, the Greeks were already using it as a fire stone, hence the name pyrite from the Greek "pyros".

Is pyrite harmful to health?

In contact with oxygen, water and humidity, pyrite oxidizes and produces sulphuric acid. The phenomenon of pyrite oxidation also leads to the formation of gypsum crystals, which increases its volume.

Unlike asbestos and lead which can be harmful to human health, pyrite is not considered a hazardous material by law. On the other hand, it can cause other types of significant problems, especially when it is present in the backfill material used under the slab of a building.

How to perform a pyrite test

To perform an iron pyrite test (which costs an average of 500 dollars), you will need to contact company that specializes in pyrite testing and follows the CTQ-M200 protocol. The company will take a sample and send it to a laboratory for analysis.

The result obtained will correspond to the swelling potential petrographic index (SPPI) of the backfill. A pyrite test with an SPPI of fewer than 10 means that the backfill does not present a major swelling risk. However, a result between 10 and 100 will indicate a greater risk.

Problems associated with pyrite-contaminated fill

Before pouring a concrete slab, crushed stone (backfill) is commonly spread to even out the surface to be covered. However, due to the chemical properties of pyrite that cause it to expand in contact with air and moisture, a fill that contains traces of this mineral could suffer from several problems.

Fill swelling

When in contact with iron pyrite, the backfill could swell and cause cracking of the basement and garage floor slabs. Damage may also occur to the foundation walls.

This process is quite slow and is sometimes only noticeable 10 years after the building was constructed. In fact, many homeowners may become aware that their residential property is contaminated when star or cross-shaped cracks appear on their concrete floors from which fine gypsum dust emerges.

Cracks in the backfill

In a finished basement, since cracks and damage to the concrete are concealed by the building materials, it is even more difficult to detect a pyrite problem in the backfill.

However, the danger is still there. Cracks in the slab can allow moisture from the soil to penetrate your home, promoting mold growth and the degradation of floor coverings. In extreme cases, swelling and cracking can even weaken the load-bearing elements of the building.

A house’s market value will therefore decrease considerably if pyrite problems have been detected and confirmed by a pyrite test.

How much does it cost to remove pyrite?

It is possible to solve a pyrite problem. However, it is a procedure that requires a lot of effort, time and resources, especially in a finished basement or garage. If you're wondering how much it costs to remove pyrite, there are several factors to consider.

First, the concrete slab covering the pyrite-containing backfill must be broken up and all contaminated soil removed. Then, DB crushed stone (certified non-swelling by its supplier) must be put back in before pouring a new concrete slab.

Removing pyrite from a garage will usually cost several thousand dollars. If access to the basement or garage is difficult, prices may increase accordingly. For more information on pricing, contact specialists.

For all your contaminated soil problems, contact EBI Enviro Urgence

To reiterate the original question, pyrite-contaminated soils are a nuisance. The longer you wait, the more iron pyrite can grow and cause significant damage to your property. The structure of the house could even be affected, depending on its construction.

Other than property damage, pyrite poses no major health risk to you or the people in your home.

If you ever have questions related to the management of hazardous materials that you do not know how dangerous they are, contact our specialists! They will be able to enlighten you and propose environmentally friendly decontamination solutions.