This Fact Sheet briefly reviews

what asbestos is, how it is identified,

where it is found, and how it is used.

The U.S. Geological Survey (USGS)

provides information on asbestos geology, mineralogy, and mining; other agencies listed on page 4 provide information on regulations and health effects of

asbestos exposure.

What is asbestos?

Asbestos is a generic name given to

the fibrous variety of six naturally

occurring minerals that have been used

in commercial products. Asbestos is

made up of fiber bundles. These bundles, in turn, are composed of extremely

long and thin fibers that can be easily

separated from one another. The bundles

have splaying ends and are extremely

flexible.

The term “asbestos” is not a mineralogical definition. It is a commercial

designation for mineral products that

possess high tensile strength, flexibility,

resistance to chemical and thermal

degradation, and high electrical resistance and that can be woven.

What minerals occur as asbestos?

The minerals that can crystallize as

asbestos belong to two groups: serpentine (chrysotile) and amphibole (crocidolite, amosite, anthophyllite asbestos,

tremolite asbestos, and actinolite

asbestos). Amphiboles are distinguished

from one another by the amount of sodium, calcium, magnesium, and iron that

they contain. Serpentine and amphibole

minerals can have fibrous or nonfibrous

structures (fig. 1); the fibrous type is

called asbestos (see sidebar on Serpentine and Amphibole Crystal Structure

and Shape).

Asbestiform varieties of several

other amphiboles have been identified.

Other minerals are similar to asbestos in

their particle shape, but they do not possess the characteristics required to classify them as asbestos (see definition of

asbestos above).

How is asbestos identified in a mineral

sample or product?

The best way to identify asbestos is

to use a microscope to examine samples

that have not been ground. Even with

finely ground samples, there is no problem identifying chrysotile because its

particle shape is distinct from the nonasbestiform varieties of serpentine.

With amphiboles, however, the distinction between asbestiform and nonasbestiform varieties is much less clear

when examining samples through a

microscope. The reason is that amphibole particles have a spectrum of shapes

from blocky to prismatic to acicular to

asbestiform. Also, amphiboles break

(or cleave) into smaller fragments when

finely ground. Long, thin cleavage fragments resemble asbestos fibers.

To resolve this problem, the analyst can compare the shapes of several

hundred amphibole particles in the

sample with those of asbestos reference

materials and determine whether a

sample is asbestiform with a fair

degree of certainty. However, unless a

fiber bundle has splaying ends, it is

impossible to determine if a single

long, thin particle grew that way (as

asbestos) or is a cleavage fragment

(nonasbestiform).

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–012–01

March 2001

Some Facts About Asbestos

Figure 1. A, Chrysotile asbestos, a member of the serpentine group of minerals. B, Antigorite and lizardite, nonasbestiform serpentine minerals. C, Tremolite asbestos, a member

of the amphibole group. D, Tremolite having a nonasbestiform habit. Serpentine and amphibole minerals can have fibrous or nonfibrous structures; the fibrous type is called asbestos.

Photographs by Garrett Hyde from U.S. Bureau of Mines Information Circular 8751, 1977.

A B

C D
Yes, the Occupational Safety and

Health Administration (OSHA) conducted a review of the health effects of

inhalation of nonasbestiform amphiboles. The agency determined (Federal

Register, v. 57, no. 10, June 8, 1992, p.

24310) that “available evidence supports

a conclusion that exposure to nonasbestiform cleavage fragments is not

likely to produce a significant risk of

developing asbestos-related disease.”

Breathing high levels of asbestos

fibers for a long time can lead to an

increased risk of asbestosis, lung cancer, and mesothelioma. Asbestosis is a

noncancerous lung disease related to

scarring of the lungs. This disease

occurs in people heavily exposed to

asbestos in the workplace and in household contacts of asbestos workers. Lung

cancer is a relatively common form of

cancer, which has been linked to smoking and a variety of occupational exposures. Cigarette smoking significantly

increases the risk of lung cancer for

people exposed to asbestos. Mesothelioma is a rare cancer of the membranes

lining the lungs, chest, and abdominal

cavity. Almost all cases are linked to

occupational asbestos exposure. The

symptoms of these diseases do not usually appear until 20 to 30 years after the

first exposure to asbestos. 

Particle shape, particle solubility,

and duration of exposure are reported to

be the three most important factors that

determine lung damage. Many

researchers believe that amphibole

asbestos particles pose a greater risk

than chrysotile particles because they

are less soluble and more rigid than

chrysotile, allowing the amphibole

asbestos particles to penetrate lung tissue and remain longer.

What is the most common type of

asbestos?

Chrysotile is the most common type

of asbestos in the United States and the

world.

als are composed of oxygen and silicon. These elements are arranged in

the shape of a pyramid or tetrahedron,

with silicon in the center and oxygen

at the four corners. For many silicate

minerals, these tetrahedra are arranged

in rows, and the rows are repeated to

form the crystal structure.

In serpentine, the element magnesium is coordinated with the oxygen

atoms in the tetrahedra. The tetrahedra

are arranged to form sheets. Serpentine is a sheet silicate.

The framework for all amphiboles is a double chain composed of

two rows of tetrahedra aligned side

by side. Attached to these tetrahedra

are elements such as aluminum, calcium, iron, magnesium, potassium, and

sodium.

Among the three principal serpentine minerals, the distinction between

asbestos and nonasbestiform varieties

is apparent. In the nonasbestiform

antigorite and lizardite, the silica tetrahedra are arranged to form a sheet

structure, and the crystals are platy;

and two longer, approximately equal

dimensions, like a saucer. 

In the asbestiform variety of serpentine, chrysotile, sheets are rolled up

tightly to form fibers.

With amphiboles, the distinction

is not so clear. When short double

chains are arranged side by side,

blocky or equant crystals form. 

If growth is along the length of the

double chains, rather than across their

width, the amphibole crystals will be

longer relative to their width. Slightly

elongated crystals are prismatic. 

As the length increases relative to the

width, the crystals are called acicular.

When the length is extremely long

compared with the width, the crystals

are called asbestiform or fibrous.

Unlike serpentine, which is either

nonasbestiform (platy) or asbestiform

(fibrous), amphiboles have a gradational transition from blocky to prismatic to acicular to asbestiform. This

gradational change makes it difficult

to distinguish between asbestiform and

nonasbestiform amphibole particles

under the microscope.
It makes up over 99 percent of present

day production in the world. Only

chrysotile is mined in the United States.

In 1999, one firm in California accounted for all U.S. chrysotile production.

Small amounts of tremolite asbestos

are mined in India and possibly a few

other countries, but production is very

limited. Commercial production of crocidolite and amosite ended about 4 years

ago in South Africa. Anthophyllite

asbestos has not been mined for an even

longer period of time in the United

States.

Where does U.S. asbestos occur?

Asbestos has been identified in 20

States (fig. 2) and mined in 17 States

over the past 100 years. It is found in

many common rocks. Serpentinite, the

most widely occurring host rock for

chrysotile, is present throughout the

Appalachians, Cascades, Coast Ranges

of California and Oregon, and other

mountain belts.

In general, chrysotile and amphibole asbestos varieties occur in areas

where the original rock, under elevated

temperatures and pressures, has been

changed by heated fluids (a process

referred to as metamorphism). This type

from California to Washington, and in

the upper Midwest in Minnesota and

Michigan. Small occurrences of asbestos

are in other areas, such as Arizona,

Idaho, and Montana.

Although asbestos can be present

in most of the metamorphic rocks

described above, the bulk of the rock

mass does not contain asbestos. In fact,

most commercial asbestos deposits contain less than 6 percent asbestos by volume. Only a few deposits contain 50

percent or more asbestos (such as

chrysotile deposits near Coalinga,

Calif.).

Is asbestos still used in the United

States?

Yes, about 15,000 metric tons (t) of

asbestos was used in the United States

in 1999; most was imported from Canada. Major manufacturing uses in the

United States are as follows: asphaltic

roofing compounds used on commercial

buildings, 61 percent; gaskets, 19 percent; and friction products, such as

brake shoes and clutches, 13 percent.

Most of these products are installed on a

commercial basis under conditions regulated by OSHA. Although very few

asbestos products have been banned in

public.

Is 15,000 metric tons a lot of

asbestos?

Relatively speaking, no. The peak

year of asbestos use in the United States

was 1973, when approximately 719,000 t

of asbestos was used for manufacturing

friction products, flooring, caulks, gaskets, packings, electrical and heat insulation, plastics, roofing, textiles, and a

host of other consumer and commercial

products.

There have been thousands of applications for asbestos. Most were viewed

as practical solutions to difficult problems. For instance, asbestos helped

make the braking systems in automobiles much more dependable, it enabled

the production of inexpensive cementbased water-supply pipes, and despite

the dire consequences to the installers,

asbestos insulation made the warships of

World War II much safer.

In the late 1960’s and early 1970’s,

the consumption of asbestos increased at

the rate of 3 to 4 percent annually. In

the 1980’s and 1990’s, consumption

declined 5 percent annually (fig. 3).

What caused the decline in asbestos

use?

Concerns over health risks posed by

high exposures to airborne asbestos

brought on much of the decline. From

the 1970’s onward, public pressure to

reduce exposure to asbestos resulted in

lowered exposure standards and spurred

the quest for alternatives to asbestos.

Exposure standards were reduced from

5 fibers per cubic centimeter (f/cc) of air

over an 8-hour time period to 0.1 f/cc in

the workplace. Also, spraying of

asbestos insulation onto steel girders

and consumer sales of raw asbestos and

artificial fireplace logs containing

asbestos were banned. Commercial

products such as asbestos-containing

insulations, plasters, ceiling tiles,

cement products, and caulks were slowly phased out. Many companies ceased

production of asbestos products because

of liability issues. As a result, asbestos

consumption in the United States

declined rapidly.

Figure 2. Occurrences of asbestos in the contiguous United States. Major asbestos-bearing

deposits occur in the mountain belts in the Eastern and Western United States. Data from

USGS Digital Data Series DDS–52 (E.J. McFaul and others, 2000, U.S. Geological Survey

Mineral Databases—MRDS and MAS/MILS).
What about worldwide use of

asbestos?

Worldwide, the use of asbestos has

declined, particularly in Western

Europe. Asbestos production is used as

a rough guide for consumption (fig. 3).

Production declined from 5.09 million

metric tons (Mt) in 1975 to about 1.93

Mt in 1999. Several Western European

countries have banned some or all

asbestos products.

In other regions of the world, there

is a continued demand for inexpensive,

durable construction materials. Consequently, markets remain strong for

asbestos-cement (A/C) products, such as

A/C panels for construction of buildings

and A/C pipe for water-supply lines.

What is the connection between

asbestos and vermiculite?

The connection between asbestos

and vermiculite was first brought to

public attention recently because of a

vermiculite mine near Libby, Mont. Vermiculite consists of clay minerals that

expand when heated to form wormlike

particles. Vermiculite is used in concrete

aggregate, fertilizer carriers, insulation,

potting soil, and soil conditioners. 

The Libby mine opened in 1921

and once accounted for almost 80 percent of the world’s vermiculite production. The Libby deposit is unique among

commercial U.S. vermiculite deposits in

having an average amphibole asbestos

content of 4 to 6 percent. Miners and

millers were, at times, exposed to high

levels of asbestos-containing dusts.

Many workers developed health problems as a result of those exposures.

Some residents of Libby who were

exposed to high levels of asbestos also

have been diagnosed with asbestosrelated symptoms.

Officials are concerned about the

asbestos content of the soils around

Libby, about workers who processed the

Libby vermiculite ore in manufacturing

plants scattered throughout the United

States, and about the customers of those

plants. USGS scientists are using a

hyperspectral remote-sensing survey of

Libby to help map the distributions of

the asbestiform amphiboles in soils.

Is this vermiculite still being sold?

The Libby vermiculite mine closed

in 1990, and shipments of vermiculite

from the Libby mill site ended in 1992.

However, products made from the Libby

vermiculite may still be available from

retailers who sell from old stocks. The

only certain way to know whether vermiculite came from the Libby mine is to

ask the manufacturer.

Yes. For questions concerning geol

ogy, mineralogy, and the asbestos industry, contact the U.S. Geological Survey

online at http://minerals.usgs.gov/minerals

or by fax from Mines FaxBack at

(703) 648–4999.

For information on regulations and

health effects of asbestos exposure, contact these agencies online:

• Consumer Product Safety Commission (www.cpsc.gov)

• U.S. Environmental Protection

Agency (www.epa.gov)

• Mine Safety and Health Administration (www.msha.gov) 

• Occupational Safety and Health

Administration (www.osha.gov)

• National Institute for Occupational

Safety and Health

(www.cdc.gov/niosh/)

• National Institutes of Health

(www.nih.gov)

For information on this Fact Sheet,

please contact:

Robert L. Virta

U.S. Geological Survey

983 National Center

Reston, VA 20192

Telephone: (703) 648–7726

Fax: (703) 648–7722

E-mail: rvirta@usgs.gov

1940 1950 1960 1970 1980 1990 1999

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

ASBESTOS, IN THOUSANDS

OF METRIC TONS

World production

Figure 3. Asbestos consumption in the United States and world production of asbestos, which

is used as a guide to world consumption. Peak U.S. consumption of asbestos was 719,000 metric tons in 1973. Peak world production was 5.09 million metric tons in 1975. Data from Minerals

Yearbook, v. I (published by the U.S. Bureau of Mines until 1995 and by the U.S. Geological Survey after 1995).