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 pHIncrease 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 limestoneBurned lime (calcium oxide) High calcium lime Dolomitic limeHydrated 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
