Crocidolite: Blue Asbestos, the Deadliest Type

Crocidolite, also called blue asbestos, is one of the six minerals regulated as asbestos under US law, and it's widely considered the most dangerous of them for causing mesothelioma (a cancer of the lining of the lungs or abdomen).¹ It was mined mainly in South Africa and Australia, with a small amount in Bolivia, and was never mined in the United States. Most American exposure came through asbestos-cement water and sewer pipe, and on a smaller scale through specialty gaskets, World War II gas mask filters and, for about four years, the filters in Kent cigarettes. People are still exposed today when old blue-asbestos pipe and building materials are cut, repaired, or torn out.

If you or a family member worked around crocidolite, or worked with asbestos-cement pipe, and you've been diagnosed with an asbestos disease, call 833-4-ASBESTOS to find out whether you have a claim.

The discovery that proved asbestos kills more than just workers

In February 1956, a young pathologist named J.C. Wagner opened the chest of a man who had died at a South African hospital. The death had been blamed on tuberculosis, a common diagnosis in that rural mining region. What Wagner found instead was something he had never seen: a massive tumor filling the entire right side of the chest, with asbestos fibers scattered through the lung.²

Over the following months, a surgeon named Paul Marchand kept sending Wagner more tissue samples from patients in the same region who were dying of what local doctors had been calling tuberculosis. A pattern emerged. These weren't infections. They were mesothelioma, a cancer so rare that most doctors had never seen a single case. And they were turning up in people who lived near the blue asbestos mines of the Northern Cape: housewives, domestic workers, farmers, cattle breeders. Many had never set foot in a mine.

In 1960, Wagner and two colleagues published their findings. They documented 33 cases of mesothelioma, all from a region where crocidolite had been mined for decades.³ The paper became one of the most cited in the history of industrial medicine, and it changed the world's understanding of the disease. Before it, mesothelioma was a rare cancer with no known cause. After it, mesothelioma had a cause: asbestos, and crocidolite above all.

What Wagner's work proved was even bigger than that. His cases included people who had never worked with asbestos a day in their lives. They had simply lived in the area and breathed the dust, or lived with a family member who carried fibers home on his clothes. Blue asbestos hadn't only sickened miners. It had killed their wives, their children, and their neighbors. Asbestos was not just a workplace hazard. It was a community-wide catastrophe.

For an overview of all six asbestos minerals and the diseases they cause, see our main asbestos minerals page.

What is crocidolite?

Crocidolite is the fibrous form of a mineral called riebeckite. It belongs to the amphibole branch of the asbestos family, which means its fibers are straight, stiff, and needle-like, the kind of shape the lungs can't clear.⁴ Of all the asbestos types, crocidolite has the finest fibers, and it's generally regarded as the most potent at causing mesothelioma.

Its most recognizable feature is its color. Crocidolite is blue, ranging from a soft lavender-blue to a deep dark blue, which is why it's known in the trade as "blue asbestos" or "Cape blue." That color comes from iron in its crystal structure. Crocidolite is also the only asbestos mineral that contains sodium. Together, the iron and sodium make the fiber chemically tough: it resists acid, and once it's in the body it resists being broken down, so it stays lodged in the lungs essentially for life.

The name comes from a Greek word for the nap or tuft on woven cloth, because when the fibers are pulled apart they separate into soft, woolly blue tufts. Two German scientists, Hausmann and Stromeyer, gave it that name in 1831.⁵

Where crocidolite came from and what it was used for

Crocidolite was never mined in the United States. It came from just a few places in the world. South Africa's Northern Cape was the main source for most of the twentieth century. Australia ran a single large mine at Wittenoom, in Western Australia, from 1943 to 1966. Bolivia had a small but strategically important deposit.⁷ South African mines were largely owned and controlled by European companies, including Cape Asbestos in Britain and the Eternit group in Belgium, a connection that has mattered a great deal in later lawsuits.

Even though it was never more than a few percent of all asbestos used, crocidolite went into a handful of very specific products because of its fine fibers, strength, filtration abilities, and chemical resistance:

• Asbestos-cement pressure pipe. This was the biggest use of crocidolite in the United States by far. Blue asbestos made water mains, sewer mains, and other pressurized pipe that ordinary asbestos couldn't match, because its stiff fibers let the wet cement drain and set much faster during manufacturing. One company, Johns-Manville, used about 62 percent of all the crocidolite in the country, by its own 1988 account, mostly for pipe, at plants in Stockton, California and Denison, Texas.⁸ CertainTeed and smaller companies made it too. The pipe plants our records name are listed below, and what the companies themselves said about the fiber is further down. A great deal of this pipe is still buried in municipal water systems, and exposure continues today as aging pipe is dug up and cut.
• Gas mask filters. During World War II, the US military used pure crocidolite to make the filters in gas masks, manufactured mainly by the Hollingsworth and Vose Company. The fiber's filtering ability was unmatched. So was its effect on the workers who handled it, as the studies below show.
• Kent cigarette filters. From 1952 to about 1956, the Lorillard Tobacco Company sold Kent cigarettes with a "Micronite" filter made from crocidolite, advertised as a health feature. For about four years, smokers breathed blue asbestos with every puff.
• Nuclear plant air filters. The same wartime filter technology, called CC-6 paper, was used to trap radioactive dust at US nuclear facilities from the early 1950s into at least 1969.
• Textiles, gaskets, packings, and spray-on fireproofing. Crocidolite's strength made it useful for woven fabrics and yarns, and its acid resistance made it useful for seals in chemical equipment and for sprayed insulation, especially in Britain and Europe.

For more on the kinds of products that contained asbestos, see our guide to asbestos-containing products.

Who was exposed to crocidolite

You may have been exposed to crocidolite if you, or someone whose dusty work clothes you were around, fits one of these descriptions:

• Worked at an asbestos-cement pipe plant, including the Johns-Manville plants in Stockton, California or Denison, Texas, or a CertainTeed plant (the plants our records name are listed below)
• Installed, cut, drilled, repaired, or removed asbestos-cement water or sewer pipe, as a water utility worker, plumber, pipefitter, or construction or demolition worker (this is the most common US crocidolite pathway, and it's still active today)
• Worked with certain acid-resistant gaskets made by companies like Garlock and Flexitallic, among others
• Made gas mask filters during World War II, especially at Hollingsworth and Vose
• Smoked Kent cigarettes between 1952 and 1956, when the filter contained crocidolite
• Worked at a nuclear facility that used CC-6 asbestos air filters
• Worked with crocidolite textiles, packings, or sprayed insulation
• Worked at, or lived near, the crocidolite mines in South Africa's Northern Cape or at Wittenoom in Australia

Family members were exposed too. Crocidolite fibers traveled home on work clothes, hair, and skin. Wives who shook out and washed laundry, and children who lived in the house, have developed mesothelioma from that secondhand exposure, often called "take-home" exposure. At Wittenoom, children were exposed simply by playing in the blue asbestos waste spread around their town.

One of the hardest things to accept about crocidolite is that it doesn't take long exposure to cause disease. As the records below show, a few months of work, or even just living nearby, has been enough.

Health risks

All forms of asbestos cause the same group of diseases: asbestosis (permanent scarring of the lungs), mesothelioma, lung cancer, and cancers of the larynx and ovary.¹ For how these diseases develop and what symptoms to watch for, see our page on asbestos-related diseases.

Crocidolite stands apart because of how potent it is and how little of it it takes.¹¹ Its fibers are the finest of the straight-fiber asbestos types, fine enough to reach the deepest parts of the lung and sharp enough to pierce the lining around it, where mesothelioma begins. And because the fiber resists being broken down, it stays there for decades, causing damage the whole time. The gap between exposure and diagnosis is long, usually 13 to 58 years,¹² which is why cases are still appearing today from exposures in the 1960s and 1970s.¹³

Wittenoom: a whole town poisoned

The mine at Wittenoom, Australia produced one of the worst health disasters ever recorded. Researchers have followed nearly 7,000 people who worked there. By 2008, 329 of them had developed mesothelioma. Put another way, 4.7 percent of workers at the mine died of mesothelioma, a cancer that strikes only about one person in 100,000 in the general population each year.¹⁴

What makes Wittenoom especially alarming is that most workers were only there briefly. Nearly three-quarters worked at the mine for less than a year before moving on. It wasn't enough to keep them safe. And the disease wasn't limited to workers, because blue asbestos tailings had been spread through the town. Residents who never worked at the mine, including children who played in the waste, developed the same diseases.¹⁵

One more pattern in the Wittenoom record is worth noting, because it shows up wherever crocidolite exposure was heaviest. Among the most heavily exposed workers, more than a third of the mesotheliomas arose in the lining of the abdomen (the peritoneum) rather than the chest; among the lighter-exposed, the share was closer to one in fifteen. The gas-mask workers described below showed the same abdominal-heavy pattern. A high proportion of peritoneal mesothelioma in an exposed group is a marker of how intense the exposure was.^14,16

The gas mask workers: months of work, decades later

During World War II, factories in Canada and Britain made gas mask filters out of pure crocidolite. Decades later, researchers went back and traced what happened to those workers. In one Canadian group of 199 workers employed between 1939 and 1942, researchers found that by 1975, 56 had died, and 9 of those deaths, about 16 percent, were from mesothelioma. Seven of the nine had worked with the fiber for less than three years. Some had worked only a few months. Workers described the factory as not even looking especially dusty.¹⁶ In that same study, mesothelioma was roughly sixty times more frequent as a cause of death among these pure-crocidolite workers than among a large Quebec chrysotile mining cohort followed over the same years, a gap that reflects those particular workforces and their very different exposures rather than a fixed potency ratio between the two fibers.¹⁶ A British factory in Nottingham showed the same pattern, with 26 mesothelioma deaths among about 1,600 workers.^17,18

These were not lifelong asbestos workers. They were ordinary people who took a wartime job for a few months, moved on with their lives, and developed a fatal cancer 20 to 35 years later.

Kent cigarettes: asbestos sold as a health feature

For about four years in the early 1950s, the crocidolite that killed gas mask workers was being put into cigarette filters. Kent's "Micronite" filter, sold from 1952 to about 1956, was made from blue asbestos and marketed as a healthier way to smoke. Smokers who chose Kent during that window inhaled crocidolite fibers directly. Mesothelioma cases have been documented in former Kent smokers whose only known asbestos exposure was the cigarettes themselves.²⁰

Disease in neighbors and families

Wagner's original South African cases were housewives, domestic workers, and farmers who had never worked with asbestos. They got sick from living in a mining region. The same pattern showed up at Wittenoom and everywhere else crocidolite was mined or processed. And family members of workers, especially wives who washed work clothes, developed mesothelioma from fibers carried home. Crocidolite has proven, again and again, that you didn't have to work with it to be killed by it.

Were you or a family member exposed to crocidolite?

If you've been diagnosed with mesothelioma, lung cancer, or asbestosis, and you think blue asbestos may have been involved, we can help you find out whether you have a claim. That includes exposure from asbestos-cement pipe work, from making or handling gas mask filters, from Kent cigarettes during the 1952 to 1956 window, from a family member's clothes, or from living near a plant that made products with crocidolite. Even brief exposure can matter, because crocidolite is so potent.

When you call, you reach our litigation team, not a screener. We'll talk through where and when you may have been exposed and explain your options. There's no fee unless we recover compensation for your family.

Call 833-4-ASBESTOS to speak with us about your case.

Is crocidolite still a danger today?

Crocidolite was the first asbestos type that governments moved to ban, a reflection of how clearly dangerous it was. The European Economic Community restricted it in 1983, years before banning the other asbestos types. Australia's Wittenoom mine closed in 1966, and Australia eventually banned all forms of asbestos by the end of 2003. In the United States, crocidolite is regulated as asbestos by the Environmental Protection Agency, the Occupational Safety and Health Administration, and others.^1,21 The EPA's 2024 rule under the Toxic Substances Control Act banned the ongoing uses of chrysotile, the only asbestos type still imported and used in the country; in a separate 2024 evaluation, the agency assessed the other five fiber types, crocidolite among them, and found that asbestos poses an unreasonable risk to health.^22,23 For where asbestos regulation stands now, see our main asbestos page.

Even so, exposure continues. The biggest ongoing source in the United States is the vast network of asbestos-cement pressure pipe still buried in municipal water and sewer systems. As that aging pipe is dug up, cut, and replaced, it releases crocidolite fibers. Exposure also happens during the demolition and renovation of older buildings and during the cleanup of contaminated sites. Because crocidolite disease can take half a century to appear, new cases from past exposure will keep emerging for years to come.

Crocidolite in the industry's own words

The asbestos industry wrote about crocidolite for decades: in its trade journal, Asbestos, in the patents it filed, and in its own letters and sworn answers. These are the documents in our library that discuss it.

In the pipe plants

The companies that made asbestos-cement pipe said in their own papers that they put blue asbestos in it:

• The government's count. By the Bureau of Mines' figures, American use of crocidolite more than tripled in five years, from 8,000 tons in 1953 to 26,000 in 1958, and "most of the crocidolite was used in making asbestos cement pipe" (Minerals Yearbook, 1958). A 1977 article in the trade journal said that in 1974 "more than 90% of the Crocidolite used in the United States went into piping applications" (Asbestos, May 1977).
• Manville's own count. A 1988 Manville internal memo said the company had used, in its own plants, "approximately 25% of the chrysotile, 23% of the amosite, and 62% of the crocidolite consumed in the United States." "The vast majority of all crocidolite used in the U.S., both by Manville and other manufacturers, was for making asbestos cement pipe," it said, and Manville was the largest maker of that pipe. Efforts to replace crocidolite with chrysotile "resulted in a poorer quality product and increased production costs."
• Johns-Manville's pipe patent. J-M's 1943 patent on asbestos-cement pipe, filed in 1941, says the inventor used "a relatively harsh, freely filtering fibre, such, for example, as crocidolite."
• Long Beach, California. A 1970 J-M memo on its workers' chest X-rays said the principal fiber at the Long Beach Pipe Plant, open since 1938, had been chrysotile, with "a small percentage of Crocidolite."
• Stockton, California. In a personal and confidential letter in 1977, J-M's president, J. A. McKinney, told the chairman of Nicolet: "Both chrysotile and crocidolite are used in the Stockton Plant." He added that exposures there had once been above the standard of the day.
• Manville, New Jersey. At an industry conference in 1980, McKinney said of the company's pipe plant there, which had "the highest incidence of disease in any plant we have had": "In making asbestos-cement pipe over a period of years we use chyrsotile mainly, but also crocidolite and amosite."
• Toronto, Canada. In 1975 Canadian Johns-Manville told the Canadian government that all the crocidolite it imported went into asbestos-cement pipe, about 8 percent of the pipe's asbestos. Without it, the company said, it couldn't make sewer pipe wider than 16 inches or pressure pipe wider than 12 to 14 inches (meeting summary). The company wrote to Ontario the same year that a ban on blue asbestos "would eliminate approximately 12,000 tons of coupling production, 25,000 tons of pressure pipe production" at its Toronto plant.
• CertainTeed. In a sworn answer in 2000, CertainTeed said that from 0 to 24 percent of the asbestos in its asbestos-cement pipe was crocidolite, by weight. It named five plants that made the pipe: Ambler, Pennsylvania; St. Louis, Missouri; Hillsboro, Texas; Santa Clara, California; and Riverside, California. CertainTeed began making pipe in 1962.

In the trade journal

The journal followed crocidolite from the South African mining fields of the early 1920s, through Australia's Wittenoom mine, wartime Bolivia and the pipe boom of the 1950s and 1960s, to the South African mills of the late 1970s. Each link opens the article's page in that issue.

• Early History of Blue Asbestos, July 1922
• Blue Asbestos Mattress Coverings, January 1923
• Asbestos in South Africa, August 1923
• Bolivia, November 1923
• Blue Asbestos in the Chemical Industry, May 1924
• Density of Blue Asbestos Deposits, November 1924
• The Mining of Blue Asbestos, September 1925
• Francis Oats, a Pioneer in the South African Asbestos Field, October 1925
• Ups and Downs of Blue Asbestos, April 1926
• Difficulties of Blue Asbestos, February 1927
• Sidelights on the Blue Asbestos Fields, January 1928
• Mining Blue Asbestos, March 1928
• White Crocidolite, October 1928
• Jottings on Blue Asbestos, May 1930
• Uses for Blue Crocidolite Asbestos, May 1935
• Mining of Blue Asbestos, April 1937
• Australian Blue Asbestos Mines, January 1939
• Bolivia, March 1941
• Union of South Africa: Its Asbestos Fields, April 1941
• Crocidolite in South Africa, July 1941
• Blue Asbestos in Australia, October 1941
• Bolivia, April 1942
• Blue Asbestos of the Hamersley Ranges, April 1942
• Asbestos Mill at Wittenoom, September 1946
• Milling Amosite and Blue, June 1950
• Present Status of Crocidolite, May 1951
• Production of Crocidolite or Blue in South Africa (I), July 1951
• Production of Crocidolite or Blue in South Africa (II), August 1951
• Spotlight on Blue Asbestos, March 1956
• Distribution of Crocidolite Asbestos, by W. E. Sinclair, September 1956
• Tiger-Eye and Its Relation to Crocidolite Asbestos, by W. E. Sinclair, November 1956
• The Economic Future of Crocidolite and Amosite Asbestos, by W. E. Sinclair, October 1957
• Crocidolite Development, November 1958
• Grading Crocidolite Asbestos, February 1959
• The Outlook for Crocidolite Asbestos, July 1960
• Crocidolite Production in South Africa and Australia, September 1963
• Amosite/Crocidolite Fact Sheet, January 1967
• Crocidolite and Amosite in Asbestos-Cement Pipe, June 1967
• Amphibole Mineral Fibers: What Purpose?, October 1967
• United Nations Assisting in Bolivia, July 1968
• Cape Asbestos Modernizes Fiber Packaging, August 1970
• Bolivian Blue Asbestos, by Dr. H. G. Klos, February 1976
• Griqualand Annual Report, 1976, September 1977
• Gefco, Blue Asbestos Producer, October 1977
• The New Pomfret Mill Complex, November 1978

In patents

111 US patents in our library mention crocidolite or blue asbestos in their text, from 1929 to 1980. At least 25 were assigned to Johns-Manville, among them the 1943 asbestos-cement pipe patent above.

References

1. IARC. Arsenic, Metals, Fibres, and Dusts. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol 100C. International Agency for Research on Cancer; 2012.
2. Wagner JC. The discovery of the association between blue asbestos and mesotheliomas and the aftermath. Br J Ind Med. 1991;48(6):399-403.
3. Wagner JC, Sleggs CA, Marchand P. Diffuse pleural mesothelioma and asbestos exposure in the North Western Cape Province. Br J Ind Med. 1960;17(4):260-271.
4. Ross M. The geological occurrences and health hazards of amphibole and serpentine asbestos. In: Veblen DR, ed. Amphiboles and Other Hydrous Pyriboles — Mineralogy. Reviews in Mineralogy. Vol 9A. Mineralogical Society of America; 1981:279-323.
5. Hausmann JFL, Stromeyer F. Beschreibung und Zerlegung des asbestartigen Krokydoliths. Ann Phys Chem. 1831;99:153-158.
6. Dana ES, Dana JD. Dana's New Mineralogy. 8th ed. Wiley; 1997.
7. Virta RL. Worldwide Asbestos Supply and Consumption Trends From 1900 to 2003. US Geological Survey Circular 1298. US Department of the Interior; 2006.
8. US Geological Survey. Minerals Yearbook: Asbestos [annual chapters]. US Department of the Interior; 1932-2024.
9. Industrial Minerals and Rocks. 4th ed. American Institute of Mining, Metallurgical, and Petroleum Engineers; 1975.
10. Bowles O. Asbestos: A Materials Survey. Information Circular 7880. US Bureau of Mines; 1959.
11. Hodgson JT, Darnton A. The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure. Ann Occup Hyg. 2000;44(8):565-601.
12. Lanphear BP, Buncher CR. Latent period for malignant mesothelioma of occupational origin. J Occup Med. 1992;34(7):718-721.
13. Reid A, de Klerk NH, Magnani C, et al. Mesothelioma risk after 40 years since first exposure to asbestos: a pooled analysis. Thorax. 2014;69(9):843-850.
14. Musk AW, de Klerk NH, Reid A, et al. Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom. Occup Environ Med. 2008;65(8):541-543.
15. Berry G, Reid A, Aboagye-Sarfo P, et al. Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up. Br J Cancer. 2012;106(5):1016-1020.
16. McDonald AD, McDonald JC. Mesothelioma after crocidolite exposure during gas mask manufacture. Environ Res. 1978;17(3):340-346.
17. Newhouse ML, Berry G. Predictions of mortality from mesothelial tumours in asbestos factory workers. Br J Ind Med. 1976;33(3):147-151.
18. Jones JSP, Pooley FD, Smith PG. Factory populations exposed to crocidolite asbestos: a continuing survey. IARC Sci Publ. 1976;(52):117-120.
19. First MW. Filters: prefilters, high capacity filters, and high efficiency filters; review and projection. In: Tenth AEC Air Cleaning Conference. US Atomic Energy Commission; 1968:65-78.
20. Selikoff IJ, Hammond EC. Multiple risk factors in environmental cancer. In: Persons at High Risk of Cancer: An Approach to Cancer Etiology and Control. Academic Press; 1975.
21. Occupational Safety and Health Administration. Asbestos. 29 C.F.R. § 1910.1001.
22. US Environmental Protection Agency. Asbestos Part 1; chrysotile asbestos; regulation of certain conditions of use under the Toxic Substances Control Act (TSCA). Fed Regist. 2024;89(61):21970-22010.
23. US Environmental Protection Agency. Risk Evaluation for Asbestos, Part 2: Supplemental Evaluation Including Legacy Uses and Associated Disposals of Asbestos. US Environmental Protection Agency; 2024.

Key Sources

Klaproth MH. Beiträge zur chemischen Kenntnis der Mineralkörper. Vol 6. Nicolaische Buchhandlung; 1815.

Lichtenstein MH. Reisen im südlichen Afrika in den Jahren 1803, 1804, 1805 und 1806. Berlin; 1811-1812.

Selikoff IJ, Lee DHK. Asbestos and Disease. Academic Press; 1978.

Badollet MS. Asbestos, a mineral of unparalleled properties. Transactions of the Canadian Institute of Mining and Metallurgy. 1951;54:151-160.

Speil S, Leineweber JP. Asbestos minerals in modern technology. Environ Res. 1969;2(3):166-208.