Morphological and chemical characteristics were determined for
airborne tungsten particles in Fallon, Nevada, a town that is
distinguishable environmentally by elevated airborne tungsten and cobalt.
From samples of airborne dust collected previously at six different places
in Fallon, tungsten-rich dust particles were isolated and analyzed with
automated electron microprobe and wavelength-dispersive spectrometry.
Representative W particles were further analyzed using transmission
electron microscopy. Morphologically, Fallon W particles are angular and
small, with minimum and maximum sizes of ≤1 μm and 5.9 μm in
diameter, respectively. The number and size of tungsten-rich particles
decrease in Fallon with distance from a hard-metal facility located near
the center of town. Chemically, Fallon airborne W particles include
mixtures of tungsten with cobalt plus other metals such as chromium, iron,
and copper. No W-rich particles were identifiable as CaWO4
(scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon
particles are most consistent with identification as tungsten carbide.
Based on these multiple lines of evidence, airborne W particles in Fallon
are anthropogenic in origin, not natural. The hard-metal facility in
Fallon processes finely powdered W and W-Co, and further investigation
using tracer particles is recommended to definitively identify the source
of Fallon's airborne tungsten.