Average EPMA chemical analyses and calculated mineral formulas.

Average EPMA chemical analyses and calculated mineral formulas of selected unexpanded vermiculite ores.

Detailed Description

Table 2.   Average EPMA chemical analyses and calculated mineral formulas of selected unexpanded vermiculite ores.

Notes: Compositions of bulk samples not individual minerals.  n = number of microprobe spot analyses collected on multiple mica flakes used to calculate the averaged composition of each sample.   ---- = not enough cation Al and/or Mg to assign to this site.  Cation sites were filled according to Deer et al. (1966).  Spectral results are consistent with some Mg in the Louisa sample occupying interlayer sites.

a Essential water = total water (released from 25 to 950 °C) minus absorbed water (released at ≤70 °C).

b Proportion of Fe3+ and Fe2+ calculated from Mössbauer analysis.

c Spectral absorptions near 3625 cm-1 indicate the presence of octahedral layer vacancies in ALB1VA00 and Zonolite® 4, with trace levels in the other two selected samples, indicating that more Mg resides in the interlayer site than is shown in the table above.  

d Interlayer water molecules per formula unit = essential water minus 4(OH) water equivalent.


Image Dimensions: 952 x 1136

Date Taken:

Location Taken: US


Characterizing the source of potentially asbestos-bearing commercial vermiculite insulation using in situ IR spectroscopy
Swayze, G.A., Lowers, H.A., Benzel, W.M., Clark, R.N., Driscoll, R.L., Perlman, Z.S., Hoefen, T.M., and Dyar, M.D., 2018, American Mineralogist, v. 103, p. 517-549.

Abstract: Commercially produced vermiculite insulation from Libby, Montana, contains trace levels of asbestiform amphibole, which is known to cause asbestos-related diseases. 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 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. 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 with a portable 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. 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 (i.e., vermiculite ore usually consists of a mixture of hydrobiotite and vermiculite mineral flakes). Band depth ratios of the 1.38/2.32-, 1.40/1.42-, and 2.24/2.38-µm absorptions allow 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. One sample of expanded vermiculite ore from multiple sources was recognized as a limitation of the spectral method, therefore an additional test (i.e., 2.24-µm absorption position vs 2.24/2.38-µm band depth) was incorporated into the spectral method to eliminate misclassification caused by such mixtures. With portable field spectrometers, the methodology developed 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.