nonmicritic

Nonmicritic is a descriptive term used in carbonate petrography to indicate rocks that do not contain a micritic (microcrystalline) carbonate mud as the dominant matrix. In contrast to micritic rocks, nonmicritic carbonate rocks show a texture dominated by coarser grains or by a sparry calcite cement rather than a fine, microcrystalline mud.

Textures and components commonly associated with nonmicritic rocks include sparite or sparry calcite cement, coarse crystalline calcite, and skeletal grains such as coral fragments, foraminifera, and bivalves. The matrix, when present, is typically relatively coarse and may be dominated by grainy or peloidal textures rather than fine micrite. In Dunham-style facies descriptions, nonmicritic rocks can be grainstones, packstones, or rudstones, depending on the relative abundance of grains to matrix and the presence of cement.

Formation and environment: nonmicritic textures often reflect higher-energy depositional settings where fine carbonate mud is limited, or they result from diagenetic processes that replace original micrite with spar cement. The absence of micrite can also arise from post-depositional dissolution or early cementation that suppresses micrite preservation.

Usage and scope: the term is primarily a petrographic and facies descriptor rather than a lithology per se. It is used alongside other texture and facies terms to characterize carbonate rocks for sedimentological, diagenetic, and reservoir-quality interpretations.

Example: a nonmicritic limestone might be a grainstone composed of skeletal grains with sparry cement and little or no micritic mud.