Types of Asbestos: The Six Minerals and How a Lab Tells Them Apart

Most pages ranking for this term are law-firm pages, and they list the six minerals in order to talk about compensation. This page does the part they skip: the exact regulatory wording, the mineralogy from USGS, what each type went into, and how a laboratory decides which one it is looking at.

The six, as the law names them

Four federal rules define asbestos, and they agree on the minerals while differing in wording that matters on a report.

Rule	Exact text	What the wording adds
AHERA, 40 CFR 763.83	“the asbestiform varieties of: Chrysotile (serpentine); crocidolite (riebeckite); amosite (cummingtonite-grunerite); anthophyllite; tremolite; and actinolite”	Asbestiform varieties only, with the mineral species named.
NESHAP, 40 CFR 61.141	“the asbestiform varieties of serpentinite (chrysotile), riebeckite (crocidolite), cummingtonite-grunerite, anthophyllite, and actinolite-tremolite”	Species first; actinolite and tremolite as one series.
OSHA, 29 CFR 1926.1101(b)	“chrysotile, amosite, crocidolite, tremolite asbestos, anthophyllite asbestos, actinolite asbestos, and any of these minerals that has been chemically treated and/or altered”	Covers treated or altered fibre, and includes PACM.
TSCA, 40 CFR 751.503	“the asbestiform variety of a hydrated magnesium silicate mineral, with relatively long and flexible crystalline fibers that are capable of being woven”	Chrysotile only, for the 2024 ban rule.

The word asbestiform carries the weight. According to USGS Open-File Report 02-149, the asbestos varieties occur as bundles of fibres that separate easily, with high tensile strength, aspect ratios from at least 20 up to 1000, and enough flexibility to be spun. The same minerals in a massive, non-fibrous habit are not asbestos under these rules.

Two mineral families: serpentine and amphibole

According to USGS Open-File Report 02-149, chrysotile is built from silicate sheets bonded to a magnesium hydroxide layer whose spacing does not quite match, so the sheets curl into tubes. Its unit fibrils are 20 to 50 nanometres across. The amphiboles are built from double chains of silicate tetrahedra, and their structure does not inherently form fibres: the asbestiform habit needs particular growth conditions.

The cleavage difference shows up in the lab. USGS notes that amphiboles cleave at about 56 degrees, so crushing a massive, non-asbestos amphibole yields fragments that look like fibres but have a much lower average aspect ratio. Telling a cleavage fragment from an asbestos fibre is one of the hard calls in amphibole analysis.

The six minerals, one by one

Type	Family and species	Trade name	Colour, per USGS	Composition
Chrysotile	Serpentine	White asbestos	White to greyish green	Hydrated magnesium silicate
Amosite	Amphibole: cummingtonite-grunerite	Brown asbestos	Yellowish grey to dark brown	Iron magnesium silicate, iron rich
Crocidolite	Amphibole: riebeckite	Blue asbestos	Cobalt blue to lavender blue	Sodium iron silicate
Tremolite asbestos	Amphibole	None given	Grey white, green, yellow, blue	Calcium magnesium silicate
Actinolite asbestos	Amphibole	None given	Greenish	Calcium magnesium iron silicate
Anthophyllite asbestos	Amphibole	None given	Greyish white, brown grey or green	Magnesium silicate with some iron

Chrysotile asbestos

The workhorse. USGS Circular 1255-KK says chrysotile occurs in larger quantities and more widely distributed deposits than any amphibole, and has softer, less harsh fibres suited to most applications. Canada, Russia, Zimbabwe and other countries mined it. It is the only type covered by the 2024 TSCA rule in 40 CFR 751 Subpart F; our asbestos ban timeline covers the dates.

Amosite

Amosite is the trade name for asbestiform grunerite. USGS says most of it came from South Africa and that it was the kind of fast-filtering, harsh fibre asbestos-cement makers preferred. USGS reported in 2002 that amosite and crocidolite were no longer mined.

Crocidolite

Crocidolite is asbestiform riebeckite, rich in iron and sodium. USGS records it from South Africa, with small amounts from Australia and Bolivia, and notes that chrysotile was once blended with it for asbestos-cement pipe strength.

Tremolite, actinolite and anthophyllite

The minor three. USGS Open-File Report 02-149 says they have had no significant industrial use in recent decades, with only small local production. Tremolite matters for another reason: USGS notes it occurs as a contaminant in other minerals, including chrysotile and talc. Most anthophyllite came from Finland and the United States, according to USGS.

How much of each was used

According to USGS Circular 1255-KK, the United States consumed about 25.6 million metric tons of chrysotile between 1900 and 2003, against 365,000 tons of crocidolite, 282,000 of amosite and 90,000 of anthophyllite. That puts chrysotile at about 97.2 percent of the US total by our arithmetic. Worldwide, USGS gives chrysotile about 96 percent of production and consumption over the same years, crocidolite 2.2 percent and amosite 1.6 percent.

Small is not the same as absent. The amphiboles total about 737 thousand tons of US consumption on the same USGS figures, and they were concentrated in particular products.

Type	US consumption, 1900 to 2003	World production, 1900 to 2003	US as share of world
Chrysotile	25,600 thousand t	173,000 thousand t	15 percent
Crocidolite	365 thousand t	3,920 thousand t	9 percent
Amosite	282 thousand t	2,810 thousand t	10 percent
Anthophyllite	90 thousand t	460 thousand t	20 percent

Which types went into which products

USGS records which fibres certain product classes used. Where a source does not name the type, the table says so rather than guessing.

Product class	Types USGS associates with it
Spray-on fireproofing and insulation, after World War II	Mainly chrysotile or amosite; crocidolite in Europe until the 1970s
Asbestos-cement pipe	Chrysotile, formerly blended with crocidolite
Asbestos-cement sheet and other products	Amosite was a preferred fast-filtering fibre, no longer used
Packings and gaskets	Mainly chrysotile in rubber
Brake linings and pads	Usually short chrysotile
Vinyl and asphalt floor tile	Type not stated in the USGS text
Talc and vermiculite	Tremolite and other amphiboles as contaminants

By about 2000 the market had narrowed. USGS Open-File Report 02-149 says industrial use had shifted almost entirely to chrysotile, and that US use was led by roofing compounds at 62 percent, gaskets at 22 percent and friction products at 11 percent.

For older products in a building, the mineral rarely changes what you do; the product type and date do. Our identification guide covers what to suspect, and the asbestos containing material page covers what the rules call each product.

Libby amphibole: the name that is not on the list

Vermiculite from Libby, Montana is the case where six names fall short. The EPA vermiculite guidance says the Libby mine supplied over 70 percent of all vermiculite sold in the United States from 1919 to 1990, often as Zonolite. USGS Circular 1255-KK, citing Meeker and others (2003), identifies asbestiform winchite, richterite, tremolite and magnesioriebeckite in the deposit.

The ATSDR Libby vermiculite summary report explains the wrinkle: the Libby amphiboles were historically characterized as a form of tremolite for industrial and regulatory purposes, and have more recently been characterized as including winchite and richterite under different International Mineralogical Association criteria. It also notes that CERCLA uses a broader definition not limited to the six commercial types.

For owners the EPA advice is the same whatever the mineral name: assume vermiculite contains asbestos and do not disturb it. Our asbestos insulation page covers that material in detail.

How PLM tells the types apart

Bulk building samples are typed by polarized light microscopy. NIOSH Method 9002, a federal bulk method similar to EPA’s, identifies all six types using morphology, refractive index, colour, pleochroism, birefringence, extinction, sign of elongation and dispersion staining. In outline: mount the sample in 1.550 liquid and look for fibres; cross the polars, because fibres that vanish at every angle are isotropic glass or mineral wool, not asbestos; check the extinction angle and the sign of elongation, which is positive for every type except crocidolite; then move through 1.700, 1.680 and 1.605 liquids for the amphiboles.

Type	Morphology, per NIOSH	Approx. refractive index	Extinction and sign	Dispersion staining colours
Chrysotile	Wavy fibres with kinks, splayed ends	1.54 to 1.55	Parallel; positive	Blue and blue magenta in 1.550
Amosite	Straight fibres, broom-like or splayed ends	1.67 to 1.70	Parallel; positive	Blue and pale blue, or gold and blue, in 1.680
Crocidolite	Straight, rigid, blue, pleochroic	1.70 to 1.71	Parallel; negative	Red magenta and blue magenta in 1.700, often hard to see
Anthophyllite	Straight fibres, cleavage fragments	1.61 to 1.63	Nearly parallel; positive	Blue and gold or gold magenta in 1.605
Tremolite	Straight and curved fibres, colourless	1.60 to 1.64	Oblique 10 to 20 degrees, sometimes parallel; positive	Pale blue and yellow in 1.605
Actinolite	Light to dark green, some pleochroism	1.62 to 1.68	Oblique; positive	Magenta and golden yellow in 1.605

The method states its own limits. NIOSH Method 9002 says fibres finer than about 0.3 micrometre will not be detected, that heat and acid treatment may alter refractive index and colour, that cellulose and wollastonite can interfere, and that floor tiles may need transmission electron microscopy for short fibres. Lab options and kits are covered on our asbestos testing kit page.

Why the regulatory definition matters on a lab report

A PLM report names a type and a percentage for each layer. Reading it against the definitions above avoids four common misreadings.

Report says	What it means under the rules
Chrysotile 2 percent	Above the 1 percent line: ACM under OSHA, AHERA and NESHAP, whatever the type.
Amosite, trace or less than 1 percent	Not ACM by definition, but NESHAP requires point counting to confirm friable results under 10 percent by visual estimate.
Tremolite in vermiculite, or none detected	EPA says testing vermiculite may give erroneous results; assume it contains asbestos.
Non-regulated amphibole, such as winchite	Outside the six-name definition in most rules, though ATSDR notes Libby material was historically called tremolite.
Fibrous non-asbestos, such as cellulose or wollastonite	Interferences NIOSH 9002 tells analysts to rule out.

Precision near the line costs money. According to the EMSL Analytical price guide, a 400 point count reports to below 0.25 percent and a 1,000 point count to below 0.1 percent, against below 1 percent for a visual estimate.

For contractors

Under federal rules the mineral type does not change the job. 29 CFR 1926.1101 applies one permissible exposure limit to asbestos as defined, all six types included, and sorts work into classes by material, not mineral. The NESHAP and AHERA thresholds treat every type alike. What type does change is the paperwork: record the type and percentage for each homogeneous area in the scope, keep the lab report with the job file, and flag any vermiculite or talc-bearing product for the abatement firm. The standards hub links the related rules, and the asbestos inspection page covers sampling.

Questions people actually ask

How many types of asbestos are there?

Six are regulated in the United States: chrysotile, amosite, crocidolite, tremolite, actinolite and anthophyllite, as listed in 40 CFR 763.83 and OSHA’s standards. USGS notes other asbestiform amphiboles exist, such as winchite and richterite found in Libby vermiculite, but they are not among the six commercial types named in most federal rules.

What are the three main types of asbestos?

Chrysotile, amosite and crocidolite, often called white, brown and blue asbestos. According to USGS, they were the three most used: chrysotile accounted for about 96 percent of world production and consumption from 1900 to 2003, crocidolite 2.2 percent and amosite 1.6 percent. Colour names are trade terms; a lab confirms type by microscopy.

What are the three categories of asbestos?

The question usually means one of two things. In mineral terms it means chrysotile, amosite and crocidolite. In EPA’s NESHAP it means the material categories: friable asbestos material, Category I nonfriable ACM such as gaskets, resilient flooring and asphalt roofing, and Category II nonfriable ACM, which is everything else that will not crumble by hand.

Which type of asbestos is most dangerous?

This page does not compare types on health grounds; see the scope note above. In regulatory terms the answer is that the rules do not rank them: OSHA, AHERA and the NESHAP apply the same 1 percent definition and the same work practices to all six types.

Is 2 percent chrysotile asbestos dangerous?

This page does not answer health questions; see the scope note above. In regulatory terms, a material with 2 percent chrysotile is above the 1 percent line, so it is asbestos-containing material under OSHA, AHERA and the NESHAP. It must be handled with the work practices its material class requires, the same as any other type at that level.

Which types of older consumer products might still contain asbestos?

EPA lists attic and wall insulation containing vermiculite, vinyl floor tiles, roofing and siding shingles, textured paint, pipe coverings, furnace gaskets, heat-resistant fabrics, and automobile clutches and brakes. The Minnesota Department of Health adds items such as fireplace decoration, gardening products with vermiculite, table pads and heat resistant gloves.

What asbestos surveys can property buyers get?

The rules describe three scopes: a survey of all accessible suspect materials in AHERA style, a pre-renovation or pre-demolition survey limited to the areas the work will touch, as the NESHAP requires for regulated buildings, and targeted sampling of one or two materials, the route OSHA allows for rebutting a presumption. Our asbestos inspection page explains what each must include.