- Folk classification
The Folk classification, devised by R. L. Folk in 1959, is a technical descriptive classification of
calcareous sedimentary rocks . It details the relative proportions ofallochems in the rock and the type of matrix. The classification scheme covers most commoncarbonate rocks , however the more inclusive although less precise alternative,Dunham classification , may be preferred in some instances.Applying Folk Classification
Folk classification consists of one or two prefixes followed by a suffix.
uffixes
The suffix "-sparite" is used if the rock has a crystalline matrix, and "-micrite" if it contains a micritic, or mud-based, matrix.
Prefixes
The prefix describing the main (non-matrix) component of the rock immediately precedes the suffix, a second prefix describing a second important component may be tagged on to the front of this.
Common Prefixes
"oo-"
Used to denote the presence of
ooids "bio-"
Used to describe biogenetic remnants - for example, shells, echinoiderm
ossicles or other tests"pel-"
Describes the presence of
peloids (fossilised droppings). May also be used to describe any pellet under 2 mm in diameter (as peloids are often hard to distinguish from intraclasts afterdiagenesis )"intra-"
Denotes the presence of
intraclasts , for example quartz grains or carbonate clasts eroded from the surrounding rocks.Example
A rock consisting mainly of ooids with some shelly fragments, with a crystalline matrix, would be termed a biooosparite.
References
*Folk, R.L., 1959, "Practical petrographic classification of limestones:" American Association of Petroleum Geologists Bulletin, v. 43, p. 1-38.
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