Asbestos is divided into two mineral groups: serpentine and 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, whose fibres are straight and stiff. The groups differ in crystal structure and chemical composition, but all six types of asbestos are carcinogenic and are all treated as asbestos.
This article covers the difference between the groups: what the names mean, why chrysotile and amphiboles have different fibres, why not all serpentines and amphiboles are asbestos and what the group means in the analysis result. The properties and uses of the individual types of asbestos are described on the page Types of asbestos.
What do serpentine and amphibole mean?
Serpentine and amphibole are broad groups of silicate minerals, not types of asbestos as such. Both groups include several minerals, and only some of them occur in nature in fibrous form, i.e. as asbestos. Asbestos is therefore a commercial term, also used in regulations, 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-rich silicates that form when magnesium-rich rock is altered by water. The most common minerals in the group, antigorite and lizardite, are not fibrous. Serpentine that has crystallised in fibrous form is chrysotile, and it is the only asbestos mineral in the group.
The amphibole group
Amphiboles are a large group of minerals found in many rocks. 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 amphiboles have different fibres?
The difference lies in the crystal structure, i.e. in 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 lie completely flat on top of each other but roll up. The result is a hollow, tube-shaped 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 the chain structure
The crystal structure of amphiboles is based on double chains running along the length of the crystal. The crystal splits along the chains, and the fibres become straight, stiff and needle-shaped. Straight fibres, which can be very thin, separate from the bundles.
Chemical difference
Chrysotile is a magnesium silicate. The composition of the amphibole asbestos types differs from type to type:
- Anthophyllite: magnesium and iron
- Tremolite: calcium and magnesium
- Actinolite: calcium, magnesium and iron
- Amosite: a lot of iron, plus magnesium
- Crocidolite: sodium and iron
It is precisely these differences in the elements that allow the laboratory to tell the types of asbestos apart.
Does the group matter for the health risk?
Amphibole fibres have been shown to remain in the lungs longer than chrysotile fibres, and the risk of mesothelioma in particular is considered higher for amphibole asbestos than for chrysotile. But this difference does not make chrysotile harmless. All six types of asbestos are carcinogenic, and the occupational safety rules for asbestos work apply regardless of the type of asbestos. If you are worried that you have been exposed, talk to a doctor.
Serpentine and amphibole in buildings
Chrysotile is the most common type of asbestos in building materials. It was used, for example, in asbestos cement, vinyl floor tiles, adhesives and roofing felt. Amosite and crocidolite were used mainly in sprayed insulation and fire protection and in industrial insulation. Tremolite and actinolite were not important commercial products but can occur as impurities in other minerals.
The type of material does not tell you which group it contains, and the same sample can contain several types of asbestos. You can read about natural occurrences in the article Asbestos in nature.
Why is the non-fibrous form an important distinction?
Because the same mineral can also occur in rock in non-fibrous form, crushed rock 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 are decisive.
How does the laboratory tell serpentine from amphiboles?
Semlab examines the samples with a JEOL SEM-EDS electron microscope according to the ISO 22262-1 standard. 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: the elemental analysis (EDS) measures the fibre's content of magnesium, silicon, iron, calcium and sodium. Their ratio shows whether the fibre is chrysotile or one of the five amphibole asbestos types.
The differences between the methods are compared in the article Asbestos analysis methods.
What does the group mean in the result?
You receive the result in English by email on the same day the sample arrives at the laboratory. It states whether asbestos was detected in the sample and, if so, which type of asbestos. The type also tells you which group the find belongs to.
- Chrysotile detected: the material contains asbestos. Removal and other work on it are planned as asbestos work.
- Amphibole asbestos detected: the measures are the same. The removal is carried out by a specialist asbestos removal contractor.
- No asbestos detected: the result applies to the sampling location and to the same material. Other materials are examined separately.
The practical measures therefore do not depend on whether the find is serpentine or amphibole. The next steps are described 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 €49.99 incl. VAT per sample. Postage is not included. You can order the analysis online, pay by card and post the sample to the laboratory as a letter or small parcel with your national postal service.