Page 170 - Petrology of Sedimentary Rocks

Transported Authigenic
Constituents Constituents
256 mm . 256 mm
1 Very coarse calcirudite I(9)
64 64 mm
Extremely coarsely
crystalline
16 mm I6 mm
Medium calcirudite (7)
4 4 mm
Fine calcirudite (6) Very coarsely crystalline
I mm I mm
Coarse calcarenite
0.5 mm (5) Coarsely crystalline
Medium calcarenite
0.25 mm 0.25 mm
Fine calcarenite
0.125 mm 7 (4) Medium crystalline
Very fine calcarenite
0.062 mm 0.062mm
Coarse calcilutite
0.031 mm - . (3) Finely crystalline
Medium calcilutite
0.016 mm -r 0.016mm
Fine calcilutite
0.008 mm *r (2) Very finely crystalline
Very fine calcilutite
0.004 mm 0.004mm
(I) Aphanocrystalline
0.002 mm-

0.001 mm= O.OOlmm
(0) Cryptocrystalline

Carbonate composition. All of the rock types described above and listed in the
table can occur either as limestone or dolomitized limestone, and some may occur as
primary dolomite. If the rock is a limestone, the rock name (e.g. oosparite or
pelmicrite) is used unmodified, intrasparrudite, for example. If the rock contains over
IO percent replacement dolomite “dolomitized” is prefixed to the main rock name (e.g.
Dolomitized Oosparite, or Dolomitized Pelmicrite). If the dolomite is of uncertain
origin, the term “dolomitic” is suggested. In case the rock is a “primary” dolomite, use
Dolomite Intramicrudite, etc.

Limestones that have been completely replaced by dolomite offer considerable
difficulty since in many cases the original structure is partly obliterated. Fine-grained
elastic particles such as pellets or finely-broken fossils are especially prone to vanish.
Likewise, one does not know the original proportion of micro-crystalline ooze versus
sparry calcite cement. In such cases it is very difficult if not impossible to allot a
dolomite to either classes I, II, or III; if ghost oolites, fossils, intraclasts, or pellets are
present, that fact can be indicated by a modifier. The crystal size of these rocks is a
very important characteristic and should be shown by the following terms and symbols:

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