3. Carbonates

Carbonate

These are sedimentary rocks composed of CaCO3 and can be clastic, bioclastic, biochemical, or chemical

Bioclastic

Erosion, transport, and cementation of fragments of shells or reefs and limestones such as stormbeds

Biochemical

Biochemical: Animals and plants calcify using CaCO3, when preserved can form biochemical sedimentary rock (coccoliths to chalk)

Chemical

Chemical: Direct CaCO3 crystals precipitate from solution (in shallow ocean, lakes, evaporites, in soils in arid regions, and in springs/caves)

Calcite

A carbonate mineral composed of calcium carbonate (CaCO3) and is the most stable form of this compound

Aragonite

The stable form of calcium carbonate (CaCO3) at high pressures; has greater hardness, less stability, and higher specific gravity than calcite

Dolomite

An anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally CaMg(CO3)2; has stronger ionic bonds and crystal structure so only effervesces with HCl when scratched into a powder

Polymorph

Minerals that have the same chemical formula but different structures

Dolomitization

Formation of dolomite from the combination or replacement of some Ca-ions with Mg-ions

Allochem

A term introduced by Folk to describe the recognizable "grains" in carbonate rocks (around 0.25 mm or larger); it is analogous to grains/fragments

Dunham Classification

Used for clastic rocks where we look at framework/clasts and matrix/cement since it is classified based on time of deposition

Folk Classification

Used for carbonates and is based on allochems, micrite, matrix, and sparite

Micrite

A dull limestone constituent formed of calcareous particles formed by the recrystallization of lime mud; particles tend to be mud-sized and settle in calm water

Sparite

Crystalline calcite, which are oftentimes sparkly with white/grey crystals, that can cement or fossilize, and are primarily precipitated calcite in voids or recrystallized with a coarse-to-fine sugary texture

Mudstone

A mud-supported sedimentary rock composed of less than 10% grains

Wackestone

A mud-supported sedimentary rock composed of more than 10% grains

Packstone

A grain-supported sedimentary rock composed of more than 10% mud

Grainstone

A grain-supported sedimentary rock composed of less than 10% mud

Boundstone

A type of sedimentary rock with its original components bound together during deposition, as shown by intergrown skeletal matter, almination contrary to gravity, or sediment-floored cavities that are roofed with organic matter and are too large to be interstices

Ooid

Sedimentary grains with concentric layers of CaCO3 which are usually less than 2 mm in diameter

Oncoid

Biologically coated grains (concentric layers of CaCO3 formed biologically) which are more than 2 mm in diameter

Pelloid

Allochems that are completely filled by micrite

Intraclast

A fragment of a carbonate sediment that has been broken up, transported, and redeposited within the same depositional area

Fossil

The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock

Intrasparite

A carbonate rock with calcite spar cement with primarily intraclastial allochems

Intramicrite

A carbonate rock with micrite matrix with primarily intraclastial allochems

Oosparite

A carbonate rock with calcite spar cement with primarily ooid allochems

Oomicrite

A carbonate rock with micrite matrix with primarily ooid allochems

Biosparite

A carbonate rock with calcite spar cement with primarily fossil allochems

Biomicrite

A carbonate rock with micrite matrix with primarily fossil allochems

Pelsparite

A carbonate rock with calcite spar cement with primarily pelloid allochems

Pelmicrite

A carbonate rock with micrite matrix with primarily pelloid allochems

Dismicrite

A type of limestone characterized by a micritic matrix that is disrupted by irregular patches of sparry calcite

Biolithite

A carbonate rock formed of organisms that grew and remained in place, comprising a rigid framework of organisms, together with associated debris