Award Date
May 2023
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Geoscience
First Committee Member
Brenda Buck
Second Committee Member
Rodney Metcalf
Third Committee Member
Pamela Burnley
Fourth Committee Member
David James
Number of Pages
165
Abstract
The presence of naturally-occurring asbestos (NOA) is increasingly concerning for scientists, health and regulatory agencies, and citizens living in impacted areas. It is commonly believed that fibrous amphibole asbestos can only form through neocrystallization. In southern Nevada, NOA occurs as a result of hydrothermal alteration of granitic rock producing fibrous amphibole both as cross-cutting neocrystallized veins and via recrystallization of original magmatic hornblende crystals. Fibers with a greater aspect ratio are known to have increased toxicity. This study measured the maximum length and average width of both neocrystallized and recrystallized fibers to see if the morphologies were similar. Neocrystallized and recrystallized fibers from the McCullough Range, NV were identified using a petrographic microscope, extracted from polished thin sections using a motorized drill, and analyzed using the scanning electron microscope (SEM), and field emission scanning electron microscope (FESEM) with energy dispersive x-ray analysis (EDS). Neocrystallization produced fibers with an average width of 0.53 ± 0.018 µm, an average length of 4.26 ± 0.257 µm, and an average aspect ratio of 8.7 ± 0.38. Recrystallization produced fibers with an average width of 0.64 ± 0.023 µm, an average length of 7.31 ± 0.483 µm, and an average aspect ratio of 13. ± 0.86. Multiple statistical analyses, explicitly the Mann-Whitney U-test, confirmed that recrystallized particles more commonly had either statistically similar (p> 0.05) or statistically wider (p< 0.05) widths, significantly longer lengths, and significantly greater aspect ratios compared to neocrystallized particles of similar mineralogy and chemistry. Because the recrystallization process produces fibers that have greater average aspect ratios, they may be more toxic than those produced through neocrystallization. We hypothesize that the likely reason for this are increased chain width defects resulting from fluctuating conditions during recrystallization. Because hydrothermal alteration and recrystallization of primary minerals is a very common geologic process, this finding may significantly increase the estimated potential of rocks and soils that contain NOA.
Keywords
Asbestos; fibrous amphibole; Naturally Occurring Asbestos; neocrystallization; NOA; recrystallization
Disciplines
Environmental Health | Environmental Health and Protection | Geology
File Format
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Renkes, Natalie G., "Morphologic Comparisons of Recrystallized and Neocrystallized Fibrous Amphibole Asbestos: Implications for Corresponding Health Risk Potential" (2023). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4766.
http://dx.doi.org/10.34917/36114791
Rights
IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/
Included in
Environmental Health Commons, Environmental Health and Protection Commons, Geology Commons