Is actinolite asbestos
UK law names asbestos actinolite. HSE's analysts' guide lists plain actinolite as its non-asbestos analogue, so a specimen's habit, not its species, decides.
Is actinolite asbestos? In UK law, only its asbestos form. Regulation 2 of the Control of Asbestos Regulations 2012 names asbestos actinolite, CAS 77536-66-4, and HSE's analysts' guide lists plain actinolite as its non-asbestos analogue. The Handbook records actinolite from bladed crystals to 15 cm through asbestiform. Which form a specimen is needs a laboratory.
In short
- The regulation names a habit, not a species. Regulation 2 of the Control of Asbestos Regulations 2012 reads asbestos means the following fibrous silicates and lists (a) asbestos actinolite, CAS No 77536-66-4 first. HSE's analysts' guide, HSG248, sets Asbestos actinolite against its Non-asbestos mineral analogue, Actinolite, and says the asbestos regulations apply only to the asbestos forms of the minerals.
- Two CAS numbers make the same point. The regulation's number for asbestos actinolite is 77536-66-4. The USGS asbestos report lists actinolite, the mineral, under 12172-67-7. The law points at a registry entry of its own for the asbestos form.
- The 3-to-20 gap: what is counted is not the same as what is asbestiform. HSG248 counts any particle longer than 5 µm, under 3 µm wide, with a length to width ratio over 3:1. It recognises the asbestiform habit by ratios of 20:1 to 100:1 or higher, fibrils and bundles. A 10 µm particle is counted at any width under 3 µm, but reaches 20:1 only at 0.5 µm or narrower, calculated.
- The actinolite sheet spans both sides. The Handbook of Mineralogy records bladed crystals to 15 cm, columnar, radiating fibrous to asbestiform, granular and massive, all as actinolite. A hand lens cannot place a specimen on that line; HSG248's methods are microscope and laboratory methods.
- No health verdict here. This page reports what the regulation and HSE's guidance say and what the sheet records. Exposure questions go to HSE and a clinician; workplace limits are in EH40 under COSHH 2002. This is not health, safety or legal advice.
| Threshold | Published criterion, as written | Source | Width a 10 µm particle must be under | What it decides |
|---|---|---|---|---|
| Countable (regulatory) fibre | Longer than 5 µm, average width less than 3 µm, aspect (length/width) ratio greater than 3:1 | HSE HSG248, A1.40 | 3 µm (the width limit binds before 3:1, which would allow 3.33 µm) | What is counted in an air sample. HSG248 notes the 3:1 ratio lets many elongated mineral fragments be counted in mining and quarrying |
| Asbestiform habit, light microscope | Aspect ratios 20:1 to 100:1 or higher for fibres longer than 5 µm; splitting into very thin fibrils; two or more of: parallel bundles, frayed ends, thin needles, matted masses, curvature | HSE HSG248, A2.41 | 0.5 µm at 20:1; 0.1 µm at 100:1 | Whether a population of fibres is asbestos rather than fragments |
| Asbestos varieties, as USGS describes them | Aspect ratios from a minimum of 20 up to 1000; high tensile strength; flexible enough to be spun; bundles easily separated | USGS OFR 02-149 | 0.5 µm at 20:1; 0.01 µm at 1000:1 | What the commercial asbestos varieties share |
| Crushed non-asbestiform amphibole | Fragments with the appearance of asbestos fibres, but an average aspect ratio considerably lower than asbestiform amphiboles | USGS OFR 02-149; HSG248, A2.57 | Often inside the 3 µm counting limit | Why counting alone cannot name the habit |
| Phase-contrast microscope (PCM) visibility | Cannot readily detect fibres less than 0.2 µm in width | HSE HSG248, 5.22 | A 100:1 fibre 10 µm long is 0.1 µm wide, below that | Why PCM counts are paired with identification methods |
Is actinolite asbestos? What regulation 2 and HSE's guide name
Definition first: in UK law the word is asbestos actinolite, and HSE's analysts' guide treats actinolite without the prefix as a different thing. Regulation 2 of the Control of Asbestos Regulations 2012, regulation 2 defines asbestos as six fibrous silicates: (a) asbestos actinolite, CAS No 77536-66-4; (b) asbestos grunerite (amosite); (c) asbestos anthophyllite; (d) chrysotile; (e) crocidolite; and (f) asbestos tremolite. The text was read on legislation.gov.uk, revised version, on 2 October 2026.
HSG248, Table A2.1, pairs each regulated variety with its non-asbestiform mineral analogue: asbestos actinolite with actinolite, asbestos tremolite with tremolite, crocidolite with riebeckite, amosite with grunerite. Paragraph A2.41 says the amphibole minerals which form asbestos also occur in non-fibrous forms, and that the asbestos regulations apply only to the asbestos forms of the minerals. That is HSE's reading of its own regulations, quoted; this page adds no interpretation to it.
The two CAS numbers. The regulation gives 77536-66-4 for asbestos actinolite. The USGS report on asbestos lists actinolite, Ca2(Mg,Fe+2)Si8O22(OH)2 as printed there, under 12172-67-7. The species itself, and the regulation as it bears on the species page, are on actinolite.
Asbestiform or massive: the habit difference, from USGS and HSE
The habit is the difference, not the chemistry. The USGS report says the difference between asbestiform and massive amphibole minerals is obvious on the macroscopic scale, although the crystalline structures of the two varieties do not exhibit substantial differences; the asbestiform amphiboles tend to have more crystal defects. It lists five asbestiform amphibole varieties, actinolite asbestos among them, and five shared properties: fibre bundles that separate easily, high tensile strength, aspect ratios from a minimum of 20 up to 1000, flexibility enough to be spun, and a resemblance to organic fibres such as cellulose.
Crushing massive amphibole makes look-alike fragments. The same report says amphiboles break along prismatic cleavages, so crushed massive, nonfibrous amphibole yields microscopic fragments with the appearance of asbestos fibres, but with a considerably lower average aspect ratio. HSG248, paragraph A2.57, says such elongated fragments can fall within the definition of a regulated fibre used for counting, and gives the optical tests an analyst uses to tell them from asbestos.
Worked: the 3-to-20 gap for a particle 10 µm long. Counting needs a width under 3 µm and a ratio over 3:1; since 10 ÷ 3 = 3.33 µm, the 3 µm width limit is the one that binds. The asbestiform criterion starts at 20:1, which is 10 ÷ 20 = 0.5 µm; at 100:1 it is 0.1 µm, below the 0.2 µm that HSG248 says phase-contrast microscopy cannot readily detect. Every particle between 0.5 µm and 3 µm wide at that length is counted without meeting the asbestiform ratio. That gap is why the analysts' guide identifies as well as counts.
What the actinolite sheet records: bladed to asbestiform
The Handbook of Mineralogy sheet for actinolite records the whole range as one species: bladed crystals to 15 cm; columnar, may be kinked or bent; radiating fibrous to asbestiform; granular to massive. Its tenacity line reads brittle, tough in fibrous aggregates (nephrite jade). Hardness is 5 to 6 and measured density 3.03 to 3.24. The formula is Ca2(Mg,Fe2+)5Si8O22(OH)2, a member of the calcic amphibole group.
The tremolite sheet, the other amphibole in this site's 176-sheet reference set, reads elongated, stout prismatic, or flattened bladed crystals, to 20 cm; also fibrous, granular or columnar aggregates. Both species are named in regulation 2 with the word asbestos in front, and both appear in HSG248's table with the plain name as the non-asbestos analogue.
A habit word on a label is not a laboratory result. HSG248's identification methods are polarised-light microscopy and, where needed, electron microscopy with analysis. This page does not offer a home test.
Is actinolite dangerous? Who answers that
This page does not say whether actinolite, or any actinolite specimen, is a health hazard. It quotes the regulation, HSE's analysts' guide and the USGS report, and reports what the Handbook sheet records. A specimen's habit, and what follows from it, are questions for a laboratory and HSE, and a concern about exposure belongs with a clinician.
Where the answers are. The HSE asbestos pages cover duties, the law and licensed work. Workplace exposure limits are in HSE EH40, and the control of hazardous substances at work falls under COSHH 2002. This site's general page is toxic minerals in a collection, and the same regulation is read against a zeolite on is scolecite asbestos. This is not health, safety or legal advice.
No handling advice is given here, deliberately. The safety and identification guides are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.