What is limestone?

Limestone = a biochemical sedimentary rock made up mostly of calcium carbonate

MineralCrystal system Formula Remarks

Calcite Rhombohedral CaCO3 Dominant limestone mineral, especially in rocks older than Cenozoic

Aragonite

Orthorhombic CaCO3 Dominant mineral in Recent carbonate sediments; alters readily to calcite

How do limestones form?Most limestones are simply the cemented remains of marine shellsLimestone “anatomy” Grains

Skeletal particles, ooids, peloids Lime mud

Microscopic crystals produced by calcareous algae and through abrasion of larger particles

Cement Inorganically precipitated CaCO3 crystals

Skeletal grains

ooids

peloids

Lime mud

Calcite cement

Factors affecting precipitation of CaCO3 in sea water

Factor Type of change Physical effect Effect on CaCO3

Temperature Increase Loss of CO2, increase in pH

Increase precipitation

Pressure Decrease Loss of CO2, increase in pH

Increase precipitation

Salinity Decrease Decrease activity of “foreign” cations

Increase precipitation

Photosynthesis Removes CO2 from sea water; pH increases

Increase precipitation

Bacterial activity

Catalyzes CaCO3 precipitation Increase precipitation

Where do limestones form?

Because CaCO3 precipitates most readily in warm, well lit, agitated water of normal marine salinity…..most limestones form in shallow, tropical depositional environments e.g., Bahamas, central America, Persian

Gulf, NW shelf of Australia, Great Barrier Reef, Malaysia, Indonesia, etc.

Modern CaCO3 depositional environments

*Note: Although cool water carbonatesAre forming in many places, they arehighly prone to dissolution and thereforedo not become major limestone accumulations

Caicos Platform

high-energysand shoals

Prevailing

winds

Reef tract

Quiet water

North America during the Devonian Period

Iowa during the Devonian Period

What are limestone products?

Whole rock Crushed limestone Dolomitic limestone

Burned lime (calcium oxide) High calcium lime Dolomitic lime

Hydrated lime (calcium hydroxide)

How is limestone used?

Construction Soil stabilization Flue Gas DesulfurizationSteel Production (flux for blast furnaces)Glass ProductionWater Treatment Waste TreatmentPaper Production (filler) Chemical Production Masonry, Mortars and Other Building Materials