Page 36 - Atlas of Sedimentary Rocks Under The Microscope

Terrigenous clastic rocks 68,69
Si ltstones

Siltstones are those terrigenous sediments in which the
majority of the grains are between 16 and 2�6 mm in
diameter (Table I , see p. 3). 68 and 69 show a coarse
siltstone (notice that the magnification is higher than that
of most of the previous photographs) with abundant
quart£ grains and thin mica flakes. The micas include
both muscovite (colourless) and biotite (yellow or
brown). Muscovite is more abundant and shows second­
order interference colours. seen in XPL. The sediment is
cemented by calcite. showing high relief in PPL and high­
order interference colours with polars crossed.

68 and 69: Axe llllll locality unknown: magn(/ication x 71:
fi8 PPI., 69 XPL.

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