Feldspar (F). Both plagioclase and K-feldspars were
observed. Plagioclase grains were recorded as euhedral, compositionally
zoned crystals to subangular grains. Twinning is
common. K-feldspar is much less common than plagioclase
and, when present, shows variable degree of roundness.
Feldspar grains may be fresh and unaltered but usually they
are replaced by carbonate or altered to sericite and clay
minerals (Fig. 5). Sandstones of the Injana Formation contain
more feldspar than the Fat’ha sandstones.