Page 138 - Petrology of Sedimentary Rocks
P. 138
MINERALOGY:
THE ARKOSE
SED. IGN. MET.
L .R.
MINERALOGY
CONTROLLED
BY
SOURCE
AREA
Arrows indicate whether constituent is increased or decreased by prolonged
abrasion. Feldspar also decreases rapidly on weathering. In diagram
above, the normal care of an acid pluton is shown, where K feldspar >>
Plagioclase. If plagioclase is subequal or dominant, it indicates either
volcanic or basic plutonic source. To distinguish these, look for volcanic
rock fragments, glass, phenocrysts, etc.
MINERALOGY \
CONTROLLED
GRAIN
vidual grains of quartz and feldspar. Volcanic rock fragments being tougher
and f iner-grained, are recognizable to much finer sizes than plutonic frag-
ments. Micas controlled by hydraulic factors. The size relationship of
feldspar and quartz depends on lenqth of abrasion.
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