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Many dctailcd limestone classifications have been proposed. The one given here (108) is one ol' the most useful and is based on the depositional texture of the rock. Ii is useful to modify this classification by adding the name of the dominant allochcm type, e.g. a sediment containing ooids cemented by sparite and lacking any carbonate mud is called an oolitie grainstone and a rock with bioclasts and carbonate mud in which the matrix supported the grains is called a bioelastie wackestone. It is often not easy to distinguish grain from matrix support in a thin section. In generał, though, sediments with morę than 55-60% grains will be grain-supporled even if not every grain is touching another in the section. Remcmber you are looking at an almost two-dimensional section and grains may be in contaet out of the piane of the section.

Limestone classification

Original components not organically bound together during deposition				Components organically bound during deposition
Contains carbonate mud			no carbonate mud	BOUND- STONE
Mud-supported		grain-supported
<10% allochems	>10% allochems
MUDSTONE	WACKESTONE	PACKSTONE	GRAIN- STONE

108 Dunhain classification of limestones according to depositional texture. Boundstoncs are scdiments in which the components arc organically bound during deposition to form a rigid structure. They include much of the sediment making up reefs and arc normally idcnti-fied at a hand-specimen levcl rather ihan microscopically.

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