Page 160 - Petrology of Sedimentary Rocks

Opal: “Opaline.”

Carbonates: “Calcitic,” “dolomitic,” “sideritic”, etc.

Iron oxides: If iron oxides from a mere superficial film or if they occur as a stain
in a red clay matrix, they are not volumetrically important enough to include as part of
the name. Only if the minerals form thick, pure colloform crusts or pore fillings should
the adjectives “hemati tic” or “limonitic” (if in doubt, “ferruginous”) be used.

Clay minerals: if the clay minerals are detrital or have formed by recrystalliza-
tion of a previous clay matrix, they are not considered as a cement, and their presence
is denoted in the maturity term. Only if they are chemical precipitates, filling previous
pore space (usually in the form of accordion-like stacks or fringing radial crusts) should
they be included as “kaolin-cemented,” “chlorite-cemented,” etc. Usually even these
are present only in small quantities and will be ignored in naming the rock.

Miscellaneous minerals: As the need arises, such terms as “pyritic,” “collophane-
cemented,” “glauconite-cemented,” “gypsiferous,” “anhydri te-cemented,” “bari tic,”
“feldspar-cemented” etc. may be used.

If there is no cement, eliminate that part of the name.

3. Textural Maturity reflects the physical characteristics and has already been
discussed at the beginning of the petrology section. The maturity term is placed third
in the rock name, because it then conveniently separates two mineral terms.

4. Miscellaneous transported constituents are often of value in interpreting
source, environment, and often are an important descriptive feature. No mineral whose
presence is already implied in the clan name is included, i.e. quartz, feldspar, and
metamorphic rock fragments are never used as modifiers. It is a matter of individual
judgment when an accessory mineral becomes of enough importance to include as part
of a fivefold name; in many rocks this part of the name may be omitted. The limits
below are reasonable suggestions.

“Chert-bearing”: Because chert is a very important mineral whose presence
indicates a sedimentary source area in part, this adjective should be used if the rock
contains more than about 5 percent chert.

“Volcani te-bear i ng”: If 2-5 percent of volcanic rock fragments or volcanic glass is
present, then this adjective is used.

“Micaceous”: This adjective is used if discrete flakes of coarse mica are
conspicuous (say l-2 percent). If desired, “muscovitic,” “biotitic” or “chloritic” may be
used if these are dominant.

“Glauconi tic”: “Cellophane-bearing,” “Fossiliferous,” etc., are used if they
constitute more than l-2 percent of the rock.

“Calcarenitic” or “calciruditic” are used if they form more than l-2 percent of the
rock. The adjective “calclithic” has been suggested for these (Anan). These terms are
used to describe reworked fragments of older limestones, eroded from terrigenous
sources. If they form penecontemporaneous limestone deposits, the terms “intraclast-
bearing,” “pelletiferous,” or “oolitic” may be used.’ If over half the transported
constitutents are reworked carbonate rock fragments, then the rocks are a member of
the calcli thi te clan.

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