Page 133 - Petrology of Sedimentary Rocks

I. Ignore the percentage of clay matrix (including micaceous hash finer than .03
mm), chemically-precipitated cements, glauconite, phosphates, fossils, heavy minerals,
mica flakes, etc. Recalculate all essential constituents (those used in giving the
sandstone clan name) to lOO%, allotting them to one of the three following poles:

Q-pole: All types of quartz including metaquartzite (but not chert).

F-pole: all single feldspar (K or NaCa), plus granite and gneiss fragments (plutonic
and coarse grained, deep-crustal rocks).

RF-pole: All other fine-grained rock fragments (supracrustal): chert, slate,
schist, volcanics, limestone, sandstone, shale, etc.

These percentages will determine which one of the seven main rock clans the specimen
falls into: If the specimen falls in the fields of Sublitharenite, Litharenite, or
Feldspathic Litharenite, then proceed to II.

II. Recalculate all fine-grained Rock Fragments to 100% and plot on the RF
triangle. This shows whether the rock isolcanic-arenite, phyllarenite, or sediment-
arenite (sedarenite??). If the latter, then go to Ill.

III. Recalculate all Sedimentary Rock Fragments to 100% and plot on the SRF
triangle. This determines whether the rock is a chert-arenite, calclithite, sandstone-
arenite or shale-arenite.

An alternative, simpler procedure would be to simply forget the daughter
triangles and name the rock according to the most abundant rock fragment.

Quartzareni te

Ss Sh
AC Sandstone-arenite,
Calc-

\‘RfT cht

\ / ASedarenite

Plagi;::;q \ “’ F,R’;itio “’

Alb & Andes.-
01 ig. Anorth.
areni te

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