What is limestone? Limestone = a biochemical sedimentary rock made up mostly of calcium carbonate MineralCrystal systemFormulaRemarks Calcite RhombohedralCaCO 3 Dominant limestone mineral, especially in rocks older than Cenozoic Aragonite OrthorhombicCaCO 3 Dominant mineral in Recent carbonate sediments; alters readily to calcite

How do limestones form? Most limestones are simply the cemented remains of marine shells Limestone “anatomy” Grains  Skeletal particles, ooids, peloids Lime mud  Microscopic crystals produced by calcareous algae and through abrasion of larger particles Cement  Inorganically precipitated CaCO 3 crystals

Skeletal grains

ooids

peloids

Lime mud

Calcite cement

Factors affecting precipitation of CaCO 3 in sea water FactorType of changePhysical effectEffect on CaCO3 TemperatureIncreaseLoss of CO 2, increase in pH Increase precipitation PressureDecreaseLoss of CO 2, increase in pH Increase precipitation SalinityDecreaseDecrease activity of “foreign” cations Increase precipitation PhotosynthesisRemoves CO 2 from sea water; pH increases Increase precipitation Bacterial activityCatalyzes CaCO 3 precipitationIncrease precipitation

Where do limestones form? Because CaCO 3 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 CaCO 3 depositional environments *Note: Although cool water carbonates Are forming in many places, they are highly prone to dissolution and therefore do not become major limestone accumulations

Caicos Platform high-energy sand 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 Desulfurization Steel Production (flux for blast furnaces) Glass Production Water Treatment Waste Treatment Paper Production (filler) Chemical Production Masonry, Mortars and Other Building Materials