Editing Limestone (section)

===Mud===
The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock.{{sfn|Blatt|Tracy|1996|p=298}} Mud consisting of individual crystals less than {{convert|5|µm|mil|abbr=in}} in length is described as ''micrite''.{{sfn|Blatt|Middleton|Murray|1980|p=460}} In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater,{{sfn|Blatt|Tracy|1996|p=300}} be secreted by algae,{{sfn|Boggs|2006|p=166}} or be produced by abrasion of carbonate grains in a high-energy environment.<ref name="trower-etal-2019"/> This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces ''microspar'', with grains from {{convert|5|to|15|µm|mil|abbr=in}} in diameter.{{sfn|Blatt|Tracy|1996|p=300}}

Limestone often contains larger crystals of calcite, ranging in size from {{convert|0.02|to|0.1|mm|mil|abbr=in}}, that are described as ''sparry calcite'' or ''sparite''. Sparite is distinguished from micrite by a grain size of over {{convert|20|µm|mil|abbr=in}} and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes.{{sfn|Boggs|2006|pp=166-167}}

Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment.{{sfn|Boggs|2006|pp=166-167}}