Xenotime is a trace mineral occurring in igneous, metamorphic and
sedimentary rocks which is resistant to weathering
and is concentrated in some beach sands. Xenotime in coal is probably
detrital in origin, having been introduced into the coal forming swamp
as extremely small waterborne and windblown grains. Xenotime is known
to have formed in sedimentary rocks, and may also have formed in coal as
an authigenic mineral precipitated from dissolved ions in the peat waters
into voids as the peat formed. Xenotime was observed in 13 of 24
coal samples in an unpublished study using scanning electron microscopy
(SEM) at the WVGES. The one micron xenotime
grain shown in this SEM image of coal is located within a small pocket
of clay minerals of detrital origin and is very likely of detrital origin.
(Dots at the bottom of the photograph are each 10 µm apart.) Xenotime
dating has recently been discovered as a way of accurately dating sedimentary
rocks, but the size and rare occurrence of xenotime in coal would make
such a use doubtful.
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