QFR - Folk's Carbonate Classification

Folk's Carbonate Classification

  • Thin-section of an oosparite with calcitic ooids and sparry calcite cement; Carmel:Formation, Middle Jurassic, of southern Utah, USA.

  • Thin section of a biopelsparite showing a geopetal structure consisting of peloid sediment and sparry calcite cement in a recrystallized bivalve shell; Bird Spring Formation (Carboniferous) of southern Nevada, USA.

  • Bioclasts in an Ordovician biosparite; T = trilobite; E = echinoderm; Ordovician of southern Ohio, USA.

  • Biomicrite

  • Micrite

  • Spar

  • Dismicrite

  • Intrasparite

  • Broken surface of Brassfield Formation (Early Silurian, Ohio) showing coarse sparry cement.


Folk's carbonate rock classification details the relative proportions of allochems in the rock and the type of matrix. The classification scheme covers most common carbonate rocks, however the more inclusive although less precise alternative, Dunham classification, may be preferred in some instances. Folk classification consists of one or two prefixes followed by a suffix.

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