Limestone

Limestone forms by sedimentation, of coral and shells (biological limestone) or by the precipitation of calcium carbonate (as calcite and aragonite), in marine waters. It comes in many forms (e.g. chalk, coquina, fossiliferous, lithographic, oolitic, travertine, tufa). It can be crystalline, clastic, granular or massive. The production of calcium oxide by roasting limestone is one of the oldest chemical transformations done by man, it is the basis of mortar and cement (calcium oxide then reacts with carbon dioxide to regenerate as calcium carbonate).

Materials are considered limestone if they have 50%+ CaO (this comes close to the ideal formula of CaCO₃). Manufacturers blend to produce a consistent product that is close to the ideal (with minimal impurities).

There are thousands of companies around the world that grind raw limestone into powders and aggregates. The powder is also called GCC (ground calcium carbonate), or just calcium carbonate. In ceramics, it is also commonly called "whiting".

GCC has countless applications, but in ceramics it is mainly used as a source of CaO (in glazes, frits, etc).

Related Information

When both mineralogy and chemistry are shown on a data sheet

Some material data sheets show both the oxide and mineralogical analyses. Dolomite, for example, is composed of calcium carbonate and magnesium carbonate minerals, these can be separated mechanically. Although this material participates in the glaze melt to source the MgO and CaO (which are oxides), it's mineralogy (the calcium and magnesium carbonates) specifically accounts for the unique way it decomposes and melts.

Idea: Gather rocks and fire them. Unexpected results!

I gathered these downstream from the Oldman River dam in southern Alberta, it exits the Rocky Mountains nearby. I want to paint on underglazes, clear glaze over them and fire to cone 4-6. Upper right: The rocks as I gathered them. Lower left: After firing to cone 04 (about 1900F). Lower right: After I poured water on them! Seven disintegrated in front of my eyes. With sound effects, high heat, even steam! That means they are all limestone or dolostone. The firing drove off the carbonate (they lost considerable weight and converted to calcium oxide, or Quicklime). When the water is added hydrated lime (calcium hydroxide) is produced. #5 and #10 cracked badly. The unfractured ones appear to be iron-bearing silt and sand stones, they can withstand considerably higher temperatures.

Links

Materials	Camadil 95 Dolomite
Materials	KARIBIB Dolomite
Materials	Limestone
Materials	Calcium Carbonate In ceramics, calcium carbonate is primarily a source of CaO in raw stoneware and porcelain glazes.
Materials	Precipitated Lime
Minerals	Gypsum Gypsum is hydrated calcium sulphate, CaSO4 2H2O. It is the crystalline mineral from which plaster is
Minerals	Aragonite A calcium carbonate mineral with a different crystal structure than calcite.
Minerals	Calcite The pure calcium carbonate crystal mineral.
Minerals	Talc Standard hydrated talc is one of a family of insoluble mineral magnesium silicates. It is a soft, gr
Minerals	Dolomite Dolomite, as a rock, is called "dolomitic limestone". It is a carbonate, similar to limestone, but h
URLs	http://www.specialtyminerals.com/our-minerals/what-is-gcc-limestone/ What is GCC at specialtyminerals.com
URLs	http://en.wikipedia.org/wiki/Limestone Limestone at Wikipedia
URLs	http://www.handbookofmineralogy.org/pdfs/Calcite.pdf Mineralogy Data for Calcite
Projects	Temperatures
Oxides	CaO - Calcium Oxide, Calcia

By Tony Hansen
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