Shown
above are thin sections of Limburgite, an augite composed of olivine and
glass-bearing, tephritic volcanic rock. The top view is shown under plane
polarized light and the bottom view under crossed polarized light. The study of
microscopic features using a polarizing or petrographic microscope is called
thin section petrography. Thin sections allow for more accurate
characterization of minerals in rock samples.
These
specimens, several millimeters across, date from the Miocene and were found in
the Kaiserstuhl Hills of southwestern Germany. Both views portray what is
called hourglass zoning. The occurrence of this mafic rock in close proximity
to the Rhine River made it convenient to quarry during the 19th century.
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