Sepiolite asbestos from Franklin, New Jersey: a case study in medical geology

Our plain-English summary of Sepiolite asbestos from Franklin, New Jersey: a case study in medical geology, by M. Germine (Environmental Research, 1987).

The study

• Author: M. Germine
• Journal: Environmental Research
• Published: 1987;42(2):386-99
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestiform sepiolite has been found in a zinc deposit at Franklin, New Jersey. The host rock is Precambrian Franklin marble. Pseudomorphous foliated texture and cross-cutting relationships indicate replacement of talc by sepiolite. Sepiolite is manganoan, while talc contains little manganese, suggesting differences in manganese substitution in these minerals and providing evidence against solid-state replacement. Sepiolite from Franklin is of moderate crystallinity and consists of soft, flexible mass-fiber. Comparison with other sepiolite samples suggests that increased crystallinity among sepiolites parallels increased fiber length, while disorder appears to be associated with flexibility. Length and aspect ratio (length/width) distributions support toxicological equation of asbestiform sepiolite with the regulated asbestos minerals. The data presented here suggest that talc can be unstable in a low-temperature hydrothermal environment, altering under certain conditions to form sepiolite. In a wider context, sepiolite may be expected to precipitate at the end-stages of hydrothermal mineralization in some talc deposits and in carbonate and calc-silicate rocks. Many occurrences of sepiolite in these rocks may have been overlooked due to similarities with other minerals. The fact that sepiolite has been previously unrecognized and misidentified at Franklin is a case in point. Since there is evidence suggesting that sepiolite is fibrogenic and carcinogenic, its potential occurrence in consumer talcs and crushed-stone products has environmental health implications. Similarities in composition and other analytical parameters may cause sepiolite to be mistaken for fibrous talc or chrysotile in environmental samples.

In plain English

This was a laboratory study of one museum specimen from the Franklin zinc deposit in New Jersey, which the museum had catalogued as serpentine. The author found it was mostly talc partly replaced by asbestiform (asbestos-like) sepiolite, a fibrous clay mineral, and described it as equivalent to mass-fiber asbestos. It was compared with an earthy, non-asbestiform sepiolite from Eski Chehir, Turkey. The sepiolite contained manganese, while the talc contained little. Electron microscope measurements of 100 fibers per sample found more than 5% of Franklin fibers longer than 8 micrometers and thinner than 0.25 micrometers, versus less than 1% in the Turkish sample. Fiber-shape measures placed the Franklin sample in the middle to upper range of asbestos samples. Under the electron microscope the sepiolite could be confused with chrysotile or fibrous talc. No people or animals were studied. Citing earlier evidence that sepiolite may be fibrogenic and carcinogenic, the author concluded that its possible presence in consumer talcs and crushed-stone products has environmental health implications.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Mineralogical laboratory study (optical microscopy, electron microprobe, X-ray diffraction, scanning and transmission electron microscopy, fiber-size measurement) of a single rock specimen. No human or animal data.
• Who was studied: One specimen of Franklin, New Jersey sepiolite and talc from the American Museum of Natural History (sample #18392). It was compared with an earthy, non-asbestiform sepiolite from Eski Chehir, Turkey, and, for X-ray diffraction, with a long-fiber sepiolite from Katonah, New York. Both comparison samples came from the Morris Museum collection.
• Exposure: No human exposure was studied. The material examined was asbestiform sepiolite replacing talc, which the author described as equivalent to mass-fiber asbestos.
• Main results:
  • The specimen had been catalogued at the museum as serpentine, apparently thought to be chrysotile asbestos.
  • Texture indicated that sepiolite had replaced talc.
  • Franklin sepiolite contained manganese (MnO 3.16% by microprobe), while Franklin talc contained little (MnO 0.23%).
  • Franklin sepiolite showed a moderate degree of crystallinity, between the earthy and the long-fiber sepiolites.
  • 100 fibers were measured on each sample.
  • In Franklin sepiolite, a large proportion of fibers had aspect ratios greater than 20, and a significant number had aspect ratios greater than 100.
  • More than 5% of Franklin sepiolite fibers were in the size range of length greater than 8 micrometers and width less than 0.25 micrometers. In the earthy Eski Chehir standard, less than 1% of fibers were in this range.
  • Franklin sepiolite had a modal aspect ratio of about 32 and a modal length of about 1.5 micrometers. The Eski Chehir standard had a modal aspect ratio of about 15 and a modal length of about 0.5 micrometers.
  • Index of fibrosity: Franklin sepiolite had m = 0.92 and r = 0.90, in the middle to upper range of asbestos samples. The Eski Chehir standard had m = 0.78 and r = 0.72, just below or in the lower range of asbestos samples.
  • Beam-damaged Franklin sepiolite resembled beam-damaged chrysotile under TEM. Step-scanning X-ray diffraction and electron diffraction were needed to confirm that chrysotile was absent.
  • Sepiolite and talc fibers could not always be told apart under TEM, which the author said could lead to underreporting of sepiolite in talcs and environmental samples.
• The authors' conclusion: The authors concluded that length and aspect-ratio distributions support treating asbestiform sepiolite toxicologically like the regulated asbestos minerals. They also concluded that sepiolite may form in talc deposits and in carbonate and calc-silicate rocks. Because these rocks are used in consumer products and crushed stone, the authors considered this to have possible environmental health implications. The toxicity evidence the author relied on came from earlier studies, not this one.
• Limitations the authors state:
  • Some water was assumed lost when the sepiolite was fused for microprobe analysis. The raw data were therefore recalculated to 100% assuming stoichiometric water content.
  • It was uncertain whether the periodic fringes seen under TEM were real structures or artifacts of electron-beam damage.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Sepiolite, Asbestiform, Talc, Mass-Fiber, Fiber Length, Flexibility, Aspect Ratio (Length-to-diameter ratio), Asbestos.

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