Asbestos is divided into two mineral groups: serpentine and the amphiboles. The only asbestos mineral in the serpentine group is chrysotile, or white asbestos, whose fibres are curly and flexible. There are five amphibole asbestos types: amosite, crocidolite, anthophyllite, tremolite and actinolite, and their fibres are straight and stiff. The groups differ in crystal structure and chemical composition, but all six types of asbestos are carcinogenic, and in Finland they are all dealt with in the same way as asbestos.
This article focuses on the difference between the groups: what the names mean, why chrysotile and amphibole fibres look different, why not every serpentine or amphibole is asbestos, and what the group means in an analysis result. The properties and uses of each individual asbestos type are on the page types of asbestos.
What do serpentine and amphibole mean?
Serpentine and amphibole are broad groups of silicate minerals, not kinds of asbestos as such. Each group contains several minerals, and only some of them occur in nature in fibrous form, that is, as asbestos. Asbestos is therefore a commercial and regulatory name for six minerals when they have crystallised as fibres. What fibrous form means is explained in the article asbestos fibres.
The serpentine group
Serpentines are magnesium silicates that form when magnesium-rich rock is altered by water. The most common minerals in the group, antigorite and lizardite, are not fibrous. The serpentine that has crystallised in fibrous form is chrysotile, and it is the only asbestos mineral in the group.
The amphibole group
The amphiboles are a large group of minerals found in many kinds of rock. Most amphiboles, such as common hornblende, occur in rock as non-fibrous crystals. Two of the five amphibole asbestos types are known by their trade names: amosite is fibrous grunerite and crocidolite is fibrous riebeckite. Anthophyllite, tremolite and actinolite are mineral names used for both the fibrous and the non-fibrous form.
Why do chrysotile and amphibole fibres differ?
The difference comes from the crystal structure, meaning how the atoms are arranged inside the mineral.
Chrysotile: tubes of rolled-up layers
The crystal structure of chrysotile consists of thin layers that do not sit perfectly flat on top of each other but curl up into a roll. The result is a hollow, tube-like fibril. In bundles, chrysotile fibres are soft, flexible and often curly, and they could even be spun and woven into textiles.
Amphiboles: straight needles from a chain structure
The crystal structure of amphiboles is built on double chains running along the length of the crystal. The crystal cleaves parallel to the chains, and the fibres are straight, stiff and needle-like. Straight fibres come off the bundles, and they can be very thin.
The chemical difference
Chrysotile is a magnesium silicate. The composition of the amphibole asbestos types varies from one type to the next:
- Anthophyllite: magnesium and iron
- Tremolite: calcium and magnesium
- Actinolite: calcium, magnesium and iron
- Amosite: plenty of iron, plus magnesium
- Crocidolite: sodium and iron
These differences in elements are exactly what allows a laboratory to tell the asbestos types apart.
Does the group matter for the health risk?
Amphibole fibres have been found to persist in the lungs longer than chrysotile fibres, and the risk of mesothelioma in particular is considered higher for amphibole asbestos than for chrysotile. That difference does not make chrysotile safe, though. All six types of asbestos are carcinogenic, and in Finland the requirements for asbestos work are the same whatever the type. The health effects are covered in the article symptoms of asbestos exposure. If you are worried about exposure, talk to a doctor or your occupational health service.
Serpentine and amphibole in Finnish buildings
Chrysotile is the most common asbestos type in Finnish building materials. It was used, for example, in asbestos cement, vinyl tiles, adhesives and roofing felt. Among the amphiboles, anthophyllite has a special place in Finland: the Paakkila mine in Tuusniemi produced anthophyllite asbestos for the domestic building industry, and old Finnish fillers often contain anthophyllite in particular. Amosite and crocidolite were used above all in sprayed insulation and fire protection and in industrial insulation. Tremolite and actinolite were not significant commercial products, but they can occur as impurities in other minerals.
You cannot tell from the type of material which group it contains, and a single sample can contain more than one asbestos type. The history of asbestos in Finland is covered in the article the history of asbestos in Finland, and natural occurrences in the article asbestos in nature.
Why the non-fibrous form is an important distinction
Because the same minerals can also occur in rock in non-fibrous form, crushed aggregate or rock dust can contain particles of tremolite, actinolite or anthophyllite, for example, that are not asbestos fibres. The name of the mineral alone therefore does not tell you whether it is asbestos. In the laboratory, both the shape of the particle and its chemical composition decide the matter.
How does a laboratory tell serpentine from amphiboles?
Onelab examines samples with a JEOL SEM-EDS electron microscope in accordance with ISO 22262-1. Identification is based on two things:
- Shape: the electron microscope image shows whether the fibres are curly, flexible bundles or straight, stiff needles, and whether they have the proportions of a fibre.
- Composition: elemental analysis (EDS) measures the fibre's content of magnesium, silicon, iron, calcium and sodium. Their proportions show whether the fibre is chrysotile or one of the five amphibole asbestos types.
The differences between methods are compared in the article asbestos analysis methods.
What does the group mean in the result?
The result is sent by email, typically on the day the sample arrives. It states whether asbestos was detected in the sample and which type. The type also shows which group the finding belongs to.
- Chrysotile detected: the material contains asbestos. Removal and any work on it are planned as asbestos work.
- Amphibole asbestos detected: the measures are the same. The removal is carried out by a company authorised for asbestos removal work.
- No asbestos detected: the result applies to the sampling spot and similar material. Other materials are tested separately.
So the practical next steps do not depend on whether the finding is serpentine or amphibole. They are covered in the article positive asbestos result, and sampling in the article how to take an asbestos sample.
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.