Micritic limestone

What is written on the plate:

Micritic limestone

This fine-grained limestone was precipitated over very long periods of time in a deep shelf sea. It contains very few fossils of organisms that inhabited the open water. Burrows traversing the rock contain dark, pyrite-rich shales that were once black clay. The finely divided pyrite weathered, leaving behind brown-colored iron oxides that give the ochre limestone its characteristic mottled structure.

Ochre limestone, Silurian, Wittgendorf, Thuringian Slate Mountains, ca. 420 Ma

Micritic limestone

Location: Wittgendorf, Thuringian Slate Mountains

Age: ca. 420 million years

Wittgendorf

Image: Google Maps

Micritic limestone is a type of rock classified in geology as limestone. Limestone is a sedimentary rock consisting mainly of the chemical compound calcium carbonate (CaCO3) in the form of the minerals calcite and aragonite[1External link]. Micrite refers to the part of limestone that consists of the smaller grain sizes and often forms the matrix of a limestone[3External link].

Micritic limestone is referred to as a solid, consolidated calcareous mud consisting of carbonate grains with a grain size of less than 63 µm. The crystal faces of micrite grains are either indistinct or invisible to the naked eye. As a result, micrite does not shine or sparkle in hand specimens. According to Folk's (1962) classification, limestones are called micritic when the bulk of the rock is composed mainly of micrite matrix (instead of the often coarser sparite cement). The rock designation of a micritic limestone depends on the nature of the coarser carbonate components surrounded by the micrite matrix: If they consist predominantly of intraskeletal fragments, they are called intramicrites. Oomicrites, pelmicrites and onkomicrites contain ooids, peloids and oncoids, respectively, in addition to micrite. Biomicrites are dominated by biogenic constituents such as shell fragments[3External link].

Limestones, including micritic limestones, have a wide economic importance as building materials in the construction industry and as natural stone. They also serve as reservoir rocks for petroleum and natural gas. Limestones can be biogenic, chemically precipitated, or clastic in origin. The composition of limestone is primarily calcite and aragonite, with varying proportions of other minerals such as clay minerals, dolomite, quartz, or gypsum[1External link][4External link]. Micritic limestones have a fine, microcrystalline structure and can be named differently depending on the nature of the included components, e.g. intramicrite, oomicrite, pelmicrite or biomicrite[3External link].

The color of limestone usually varies from white to ocher, depending on the presence of manganese, iron oxides, and other colored minerals. Limestone has a relatively low hardness of 3 on the Mohs scale and a density of 2.6 to 2.9 kg/dm3 for dense (non-porous) limestone[1External link].

Location of the rock "Micritic limestone" near the village Wittgendorf

Image: Thomas Voigt