Asbestos is a naturally occurring mineral. It forms in the bedrock in certain types of rock, when the rock is altered by heat, pressure and water and some of its minerals crystallise into thin fibres. Asbestos ended up in buildings when these fibre deposits were mined and the fibre was mixed into fillers, adhesives, boards and insulation. At home, then, you almost always come across asbestos in manufactured building products, not in natural stone.
This article explains which rocks asbestos forms in, where it has been mined, how the Finnish bedrock fits into the picture and what naturally occurring asbestos means for someone living in or renovating an ordinary house.
How does asbestos form in nature?
Asbestos is not a single substance but a collective name for six silicate minerals that can crystallise in fibrous form. Fibres only form under particular conditions. Typically this happens when a rock is altered deep in the Earth's crust by heat, pressure and circulating fluids. The fibres often grow in cracks and veins in the rock, from which they can be pulled out in bundles.
- Serpentine asbestos, or chrysotile, forms in serpentinite, a rock altered from magnesium-rich rock. Chrysotile fibres are curly and flexible.
- The amphibole asbestos types, amosite, crocidolite, anthophyllite, tremolite and actinolite, form in altered rocks, and their fibres are straight and stiff.
The differences between the two groups are covered in more detail in the article serpentine and amphibole asbestos, and the definition of a fibre in the article asbestos fibres.
The same mineral can be a fibre or ordinary rock
Most asbestos minerals also occur in nature in a non-fibrous form. Tremolite, actinolite and anthophyllite, for example, are common minerals in many types of rock, and most of the time they occur as ordinary crystals rather than fibres. A mineral only counts as asbestos once it has crystallised into thin fibres. That is why the name of a rock or mineral does not by itself tell you whether asbestos is involved.
Where has asbestos been mined?
Commercially significant asbestos deposits exist in only a handful of places, and world production was concentrated in a few countries. Chrysotile has been by far the most commonly mined type. Finland imported chrysotile mainly from Canada and the Soviet Union, and it was used, for example, in asbestos cement boards. Amosite was mined mainly in South Africa, and crocidolite in South Africa and Western Australia.
Tremolite and actinolite were generally not mined as asbestos. They ended up in products mainly as impurities in other minerals, such as chrysotile, vermiculite or talc, because they occur in the same rocks in nature.
Asbestos in the Finnish bedrock
Finland is an unusual country in the history of asbestos, because it mined its own. The Paakkila mine in Tuusniemi produced anthophyllite from 1918 to 1975, and in its day it was the largest anthophyllite mine in the world. The fibre went mainly to the domestic construction industry. This is why the asbestos in old Finnish fillers is often anthophyllite rather than chrysotile. Read more on the anthophyllite page and in the article the history of asbestos in Finland.
Besides Paakkila, the Finnish bedrock contains rocks in places where asbestos minerals can occur naturally. In intact bedrock the fibres stay locked inside the rock. It becomes relevant when such rock is quarried, crushed or drilled, because fibres can then be released with the dust. That is why naturally occurring asbestos is taken into account in, for example, the production of crushed rock aggregate and in mining.
Is naturally occurring asbestos a danger at home?
In everyday living, naturally occurring asbestos is generally not the thing to worry about. The asbestos risk in a home is almost always linked to old building products to which the fibre was added on purpose: fillers, tile and floor adhesives, asbestos cement boards, pipe insulation and vinyl tiles. These are covered in the article where there may be asbestos.
The health risk is the same wherever the fibre comes from. All types of asbestos are carcinogenic, and the danger arises when fibres get into the air you breathe. An intact material or intact rock does not release fibres. If you are worried about possible exposure, talk to a doctor or your occupational health service.
How does the laboratory tell asbestos apart from other fibres?
Because the same mineral can be a fibre or ordinary rock, and nature also has many other fibrous minerals, asbestos cannot be identified by its appearance. Onelab examines samples with a JEOL SEM-EDS electron microscope in accordance with ISO 22262-1. The microscope image shows the shape of the fibre, and the elemental analysis shows its chemical composition. Together they distinguish the six asbestos minerals from one another and from other fibres, such as glass wool and stone wool.
What should you do if you suspect asbestos in a material at home?
If your renovation involves a material installed before 1994, test it before it is sanded, drilled or demolished. You can take the sample yourself:
- Wear disposable gloves and a respirator of at least class FFP3.
- Mist the sampling spot with a spray bottle to keep dust to a minimum.
- Remove a piece of about 2–5 centimetres so that every layer comes with it, down to the substrate.
- Put the piece in a zip-lock bag, seal it and pack it inside a second bag.
- Mark the bag with the sample location and material.
- Cover the sampling spot with tape and wipe the area with a damp cloth.
More detailed instructions are in the article how to take an asbestos sample. The result is sent by email, typically on the day the sample arrives. If asbestos is detected, the removal is carried out by a company authorised for asbestos removal work.
How much does an asbestos analysis cost?
The analysis costs €39.90 + VAT per sample, and the price is the same for 1–100 samples. Orders of more than 100 samples can be priced separately. Postage is not included. You can order the analysis online and send the sample to the laboratory by post.