Straight to slightly undulose extinction is present, suggesting
a plutonic igneous origin. Quartz grains may or may not have
inclusions. The most common inclusions are zircon, rutile, iron
oxides and vacuoles, which are distributed in an oriented or
random pattern, suggesting a metamorphic or plutonic igneous
origin. Qm is usually in the form of subangular to subrounded
and occasionally well-rounded grains indicating the reworked
sedimentary origin. Most polycrystalline quartz grains (Qp)
consist of more than three crystals. The contacts between the
subgrains are straight to sutured, the latter being more
common. The subgrain size is variable, even within a single
composite grain of Qp. Chert (microcrystalline Qp) is common
(Fig. 5).