Using In Situ IR Spectroscopy Measurements of Vermiculite Insulation to Determine Its Origin

Science Center Objects

The goal of this study was to determine if in situ near-infrared reflectance measurements, using portable spectrometers, could be used to reliably identify the source of vermiculite ore and therefore its potential to contain asbestos. The method developed can be used to determine vermiculite insulation's source and estimate its potential amphibole content, providing low-cost analysis with onsite reporting to property owners.

Photo of Vermiculite Attic Insulation from Libby, Montana

Photo of Vermiculite Attic Insulation from Libby, Montana. Li2UI = Libby sample 2 from University of Idaho. Sample courtesy of Mickey Gunter, University Distinguished Professor Emeritus.

(Credit: Gregg Swayze, USGS. Public domain.)

Scientific Issue and Relevance

Approximately one million homes in the U.S. contain expanded  vermiculite attic insulation. One of the major past sources of this vermiculite was commercially produced vermiculite insulation from Libby, Montana, which contained trace levels of asbestiform amphibole, which is know to cause asbestos-related diseases. Although the Libby mine is closed and part of a Superfund site, existing insulation in older homes and buildings still needs to be tested for asbestos. When vermiculite insulation is found in a building, evaluation for its potential asbestos content traditionally involves collecting a sample from an attic or wall and submitting it for potentially time-consuming analyses at an off-site laboratory. The need for asbestos screening is likely to increase as the public becomes aware of the potential health issues posed by exposure to elongate amphiboles during home improvements or maintenance in areas with vermiculite insulation or potential liability of owning property containing vermiculite insulation from Libby. Given the large number of buildings potentially requiring vermiculite insulation asbestos screening, use of an in situ analytical method can save time, eliminate the need for transport and disposal of hazardous samples, and thereby reduce the cost and lag time of screening.

Methods to Address Issue

The goal of this study was to determine if in situ near-infrared reflectance measurements could be used to reliably identify the source of vermiculite ore and therefore its potential to contain asbestos.  Reflectance spectra of 52 expanded ore samples, including attic insulation, commercial packing materials, and horticultural products from Libby, Montana; Louisa, Virginia; Enoree, South Carolina; Palabora, South Africa; and Jiangsu, China, were measured in a laboratory setting with a portable field spectrometer.

The mine sources for these vermiculite ores were identified based on collection location, when known, and on differences in elemental composition as measured by electron probe microanalysis. Selected unexpanded vermiculite ore samples, and as needed, about a third of the expanded vermiculite ore samples and mineral sink fractions were analyzed using X-ray diffraction.  

Reflectance spectra of the insulation samples show vibrational overtone and combination absorptions that vary in wavelength position and relative intensity depending on elemental composition and proportions of their constituent micas. Band depth ratios of the 1.38/2.32-, 1.40/1.42-, and 2.24/2.38-µm absorptions allowed determination of a vermiculite insulation’s source and detection of its potential to contain amphibole, talc, and/or serpentine impurities. Spectroscopy cannot distinguish asbestiform vs non-asbestiform amphiboles. However, if the spectrally determined mica composition and mineralogy of an insulation sample is consistent with ore from Libby, then it is likely that some portion of the sodic-calcic amphibole it contains is asbestiform, given that all of the nearly two dozen Libby vermiculite insulation samples examined with scanning electron microscopy in this study contain amphiboles.

Key Findings

Overall, elongate particles in the relatively abundant Libby amphibole bundles are consistently thinner and longer than those found more rarely in the sink fractions of expanded ore samples from the three-other major historical sources. All of the nearly two dozen Libby vermiculite insulation samples examined with scanning electron microscopy in this study contained asbestiform amphiboles compared to relatively little asbestos to none in samples from the other locations. Spectroscopy accurately determined the origin of the vermiculite insulation samples. With portable field spectrometers, the methodology developed from this study can be used to determine vermiculite insulation’s source and estimate its potential amphibole content, thereby providing low-cost analysis with onsite reporting to property owners.  

 

Return to Spectroscopy Laboratory | Geology, Geophysics, and Geochemistry Science Center