Is tremolite asbestos?
Tremolite is a mineral; asbestos tremolite is named in UK law. USGS puts it under 500 MPa in tension; HSE says optics may not tell it from actinolite.
Tremolite is a mineral species; asbestos tremolite, CAS No 77536-68-6, is item (f) of the six fibrous silicates in regulation 2 of the UK Control of Asbestos Regulations 2012. The Handbook records tremolite as crystals to 20 cm and as fibrous aggregates. Which form a specimen is needs a laboratory. This page gives no safety verdict.
In short
- What the law names. The Control of Asbestos Regulations 2012, regulation 2 reads: asbestos means the following fibrous silicates, and lists (a) asbestos actinolite, (b) asbestos grunerite (amosite), (c) asbestos anthophyllite, (d) chrysotile, (e) crocidolite and (f) asbestos tremolite, CAS No 77536-68-6. The word is asbestos tremolite; the species is tremolite, whose sheet records crystals to 20 cm and fibrous aggregates.
- The 500 line. The USGS asbestos report (Virta 2002) tabulates four asbestos types. Tremolite asbestos: tensile strength under 500 MPa, flexibility poor and generally brittle, spinnability poor. The other three start at 1100 MPa (chrysotile), 1500 (amosite) and 1400 (crocidolite): tremolite’s ceiling is 0.45 of the lowest of those floors. Virta says tremolite has essentially no industrial application but may be found as a contaminant in chrysotile and talc.
- The 1.605 problem. HSE HSG248, Asbestos: The Analysts’ Guide (second edition, 2021) identifies asbestos types with dispersion-staining liquids: 1.550 for chrysotile, 1.605 for tremolite and anthophyllite, 1.640 for actinolite, 1.670 for amosite, 1.700 for crocidolite. It says optics alone may not distinguish tremolite from actinolite, a continuous solid-solution series, or from anthophyllite, and that electron microscopy, X-ray diffraction or infrared spectroscopy are used when it matters.
- Documented case: Libby. The USGS record of Meeker et al. (2003), American Mineralogist 88, 1955 records 30 amphibole-rich samples from the Rainy Creek complex near Libby, Montana, identified as winchite, richterite, tremolite and magnesio-riebeckite in nearly complete solid solution, from prismatic to asbestiform. Of those four, regulation 2 names only tremolite. HSG248 says other non-regulated amphiboles also occur in the asbestiform habit and are outside its scope.
- No verdict here. This page does not say tremolite, or any tremolite specimen, is or is not safe, and gives no handling, cutting, cleaning or storage advice. Exposure questions go to the HSE asbestos pages and a clinician; workplace limits are in HSE EH40 under COSHH 2002. This is not health, safety or legal advice.
| Property | Chrysotile | Amosite | Crocidolite | Tremolite asbestos |
|---|---|---|---|---|
| Named in regulation 2 as | (d) chrysotile | (b) asbestos grunerite (amosite) | (e) crocidolite | (f) asbestos tremolite, CAS No 77536-68-6 |
| Mineral group (Virta) | Serpentine | Amphibole | Amphibole | Amphibole |
| Tensile strength, MPa (Virta) | 1100 to 4400 | 1500 to 2600 | 1400 to 4600 | Under 500 |
| Flexibility (Virta) | High | Fair | Fair to good | Poor, generally brittle |
| Spinnability (Virta) | Very good | Fair | Fair | Poor |
| Hardness, Mohs (Virta) | 2.5 to 4.0 | 5.5 to 6.0 | 4.0 | 5.5 |
| Specific gravity (Virta) | 2.4 to 2.6 | 3.1 to 3.25 | 3.2 to 3.3 | 2.9 to 3.2 |
| Refractive index (Virta) | 1.53 to 1.56 | 1.63 to 1.73 | 1.65 to 1.72 | 1.60 to 1.64 |
| HSG248 dispersion-staining liquid | 1.550 | 1.670 | 1.700 | 1.605, shared with anthophyllite |
| World production, 2000 (Virta, Table 1) | Over 99% | None | None | Insignificant |
| Major sources (Virta, Table 1) | Russia, Canada, China, Brazil, Kazakhstan, Zimbabwe | Deposits in South Africa | Deposits in South Africa | Deposits in India, Italy, Korea, Pakistan, South Africa |
Is tremolite asbestos? What regulation 2 and HSE name
Tremolite is a mineral species; regulation 2 names asbestos tremolite, and HSE describes asbestos as the fibrous forms of the minerals it lists. The Control of Asbestos Regulations 2012, regulation 2(1), in the revised text on legislation.gov.uk read on 16 October 2026, says asbestos means the following fibrous silicates: (a) asbestos actinolite, CAS No 77536-66-4; (b) asbestos grunerite (amosite), CAS No 12172-73-5; (c) asbestos anthophyllite, CAS No 77536-67-5; (d) chrysotile, CAS No 12001-29-5 or CAS No 132207-32-0; (e) crocidolite, CAS No 12001-28-4; and (f) asbestos tremolite, CAS No 77536-68-6.
HSE’s reading. HSG248 opens its identification appendix by calling asbestos a general term for the fibrous forms of several naturally occurring silicate minerals, and says that for regulatory purposes the regulations define asbestos as any of the six or any mixture of them. Its pairing of each regulated variety with a non-asbestos analogue, and the counting thresholds, are set out on is actinolite asbestos and are not repeated here.
What the tremolite sheet records. Elongated, stout prismatic or flattened bladed crystals to 20 cm; also fibrous, granular or columnar aggregates; hardness 5 to 6; density 2.99 to 3.03. The sheet does not use the word asbestiform. The IMA list gives tremolite as ☐Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2, Rd, 2012 s.p., Switzerland. The species page is tremolite.
How is tremolite asbestos different from chrysotile or crocidolite? The 500 line
On the USGS figures, tremolite asbestos is the weakest and least spinnable of the four asbestos types tabulated: under 500 MPa in tension against at least 1100 for the others. Virta’s Table 4, Physical and Chemical Properties of Asbestos Fibers, gives tremolite asbestos flexibility poor, generally brittle; texture generally harsh; spinnability poor; tensile strength under 500 MPa. Chrysotile is 1100 to 4400, amosite 1500 to 2600, crocidolite 1400 to 4600. Worked: 500 / 1100 = 0.45, so tremolite’s ceiling is under half the lowest floor of the other three; crocidolite’s top figure is 9.2 times it.
Why that matters to the record, not to the risk. Virta says the asbestos varieties share fibre bundles that separate easily, high tensile strength, aspect ratios of at least 20 up to 1000, flexibility enough to be spun, and a resemblance to organic fibres. His own table scores tremolite asbestos low on two of those. He says tremolite has essentially no industrial application but may be found as a contaminant in other fibres or industrial minerals, naming chrysotile and talc, and that actinolite, anthophyllite and tremolite asbestos may still be mined in small amounts for local use. None of this is an exposure finding, and this page draws none from it.
Where it was produced. Virta’s Table 1 lists tremolite deposits in India, Italy, Korea, Pakistan and South Africa, with world production in 2000 insignificant, against over 99% for chrysotile; his Table 3 gives one analysis, from Pakistan: SiO2 55.1%, MgO 25.7%, CaO 11.5%.
Can a laboratory tell tremolite from actinolite? The 1.605 problem
Not always by optics: HSE’s analysts’ guide says polarised-light work may not separate tremolite from actinolite or anthophyllite. HSG248, paragraph A2.54, gives the theoretical liquids for dispersion staining: 1.550 for chrysotile, 1.605 for tremolite and anthophyllite, 1.640 for actinolite, 1.670 for amosite and 1.700 for crocidolite, adding that fibre composition varies by source and a wider range of liquids may be needed. Paragraph A2.56 says optical properties alone may not be sufficient to distinguish tremolite from actinolite, because they form a solid-solution series with a continuous range of indices, or from anthophyllite, because birefringence and index ranges are similar.
What the sheets show. The Handbook gives tremolite α 1.605 to 1.613 and actinolite α 1.613 to 1.646: the two ranges meet at 1.613. Virta gives tremolite asbestos 1.60 to 1.64 overall. HSG248 says that where the distinction is critical, analytical electron microscopy, X-ray diffraction or infrared spectroscopy should be used, and paragraph A2.4 lists fibres below about 1 µm wide as another difficulty.
What that means for a label. Tremolite, actinolite and anthophyllite asbestos are all named in regulation 2, so the boundary changes the mineral name, not whether the regulation names it. A label is not a laboratory result either way, and this page offers no home test. The same regulation is read against actinolite on is actinolite asbestos, against a zeolite on is scolecite asbestos and against a quartz gem on is tiger’s eye asbestos.
When the answer changes: the Libby amphiboles, a documented case
An amphibole that grows in the same series as tremolite need not be one of the six names in regulation 2. The USGS record of Meeker and co-authors (American Mineralogist 88, 1955, 2003) describes 30 amphibole-rich rock samples from the vermiculite deposit in the Rainy Creek alkaline-ultramafic complex near Libby, Montana. Electron probe and X-ray diffraction work found winchite, richterite, tremolite and magnesio-riebeckite, with nearly complete solid solution between them, and morphologies from prismatic crystals to asbestiform fibres, most intermediate between the two.
Against the regulation. Of those four, regulation 2 names tremolite, as asbestos tremolite. It does not name winchite, richterite or magnesio-riebeckite; crocidolite, which it does name, is the asbestiform riebeckite of HSE’s table. All four have IMA rows: winchite, Rd 2012 s.p., India; richterite, Rd 2012 s.p., Sweden; magnesio-riebeckite, Rd 2012 s.p., Japan. HSG248, paragraph A2.4, says other non-regulated amphibole minerals are also known to occur in the asbestiform habit but their identification is not within its scope, and Virta records potassian winchite with an asbestiform habit from western Texas.
Why a collector meets these names. The tremolite sheet lists riebeckite and winchite among tremolite’s associates. HSG248, paragraph A2.57, names dolomite, basalt, soapstone (talc), marble and vermiculite as rocks and minerals that can on occasion carry small amounts of amphibole asbestos or chrysotile as a natural impurity. Those are statements about geology from the sources, quoted; they are not an assessment of any specimen.
Is tremolite dangerous? Who answers that
This page does not say whether tremolite, or any tremolite specimen, is safe or dangerous to handle, keep, cut or clean. It quotes the regulation, HSE’s analysts’ guide and two USGS sources, and reports what the Handbook sheet records. None of those sources assesses the exposure from a mineral specimen, and a mineral being named in a regulation is not by itself an exposure finding either way.
Where the answers are. The HSE asbestos pages cover the dangers, the duty to manage asbestos in buildings, licensable work and the law under the Control of Asbestos Regulations 2012. Workplace exposure limits are in HSE EH40, and hazardous substances at work fall under COSHH 2002. A concern about your own exposure belongs with a clinician. The site’s general page is toxic minerals in a collection. This is not health, safety or legal advice, and 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.