Dolomite

Dolomite, as a rock, is called "dolomitic limestone". It is a carbonate, similar to limestone, but having the chemistry CaMg(CO₃)2 (instead of CaCO₃). Manufacturers blend materials in a controlled fashion to produce a consistent product having the ideal mix of calcium and magnesium carbonates to approximate the formula CaMg(CO₃)2.

In ceramics, dolomite powders are the most inexpensive source of MgO and CaO for glazes and frits.

Related Information

Idea: Gather rocks and fire them. Unexpected results!

This picture has its own page with more detail, click here to see it.

I gathered these downstream from the Oldman River dam in southern Alberta, not far from where the river exits the Rocky Mountains (it cuts through many different rock strata upstream, including both limestone and dolostone, as well as quartz sandstone and siltstone). Upper left: The gravel bar where I collected them. Upper right: The rocks as gathered. Lower left: After firing to cone 04 (about 1900°F). Lower right: After I poured water on them!

Seven disintegrated before my eyes—with sound effects, intense heat and even steam! That identifies them as carbonate-rich rocks, likely limestone or dolostone. Firing drove off their CO2 and caused considerable weight loss, converting the calcium carbonate to calcium oxide—quicklime. Dolostone also produces magnesium oxide. When water was added, the CaO rapidly hydrated to calcium hydroxide, releasing enough heat to break the rocks apart. Two others cracked badly just from the firing. The survivors appear to be more silicate-rich siltstones and sandstones—and some of them can withstand considerably higher temperatures.

The exciting part of this: A river gravel bar is really a randomly assembled collection of ceramic raw materials. Next project is to fire more rocks to cone 6 and 10.

Links

Materials	Dolomite An inexpensive source of MgO and CaO for ceramic glazes, also a highly refractory material when fired in the absence of reactant fluxes.
URLs	http://www.mineralszone.com/minerals/dolomite.html Dolomite at mineralszone.com
URLs	http://www.handbookofmineralogy.org/pdfs/Dolomite.pdf Dolomite mineral data
URLs	https://en.wikipedia.org/wiki/Dolomite_(rock) Dolomite rock at Wikipedia
Minerals	Limestone Limestone forms by sedimentation, of coral and shells (biological limestone) or by the precipitation
Minerals	Talc Standard hydrated talc is one of a family of insoluble mineral magnesium silicates. It is a soft, gr
Minerals	Calcite The pure calcium carbonate crystal mineral.
Oxides	CaO - Calcium Oxide, Calcia

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By Tony Hansen
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