Magnesium Carbonate
MgCO3, Magnesite
Chemistry
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Volatiles
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Miscellaneous
- Family: Flux Source
- Region: North America
- Mined At: Unspecified
- Raw Mineral: No
- Generic: Yes
Notes
See also Light Magnesium Carbonate.
Magnesite is used in pottery bodies, glazes, and glass. It is quarried in California, Washington, Austria, Russia, Manchuria, Greece and Slovakia and processed from sea water. Sources are reasonably consistent in the CO2 content, but can vary widely in the iron and significantly in the MgO.
Magnesite decomposes at 900C, losing its carbon dioxide.
Heavy and light varieties are available. Light magnesium carbonate or hydromagnesite is made by boiling together solutions of magnesium sulfate and sodium carbonate. Light magnesium carbonate is used as a electrolyte in both ground and cover coat enamels. It is added (.12-.25%) to flocculate clay slurries, improving and stabilizing the set and suspension characteristics.
Magnesium carbonate by itself is very refractory, and is used to make bricks for the cement and metal industries. It is 'dead burned' in rotary kilns, then reground, sized, and dry pressed using organic binders.
Magnesite is used in low fire glazes in to produce opacity and matteness.
Dolomite and talc are more practical sources of MgO for most higher temperature applications.
In glaze melts it is an active flux at higher temperatures (2150C+), and it produces elasticity, a lower expansion coefficient and smooth buttery surfaces. At lower temperatures it is a refractory and will matte glazes and make them crawl due to its high shrinkage and contributions to the suface tension of the melt.
Magnesite is also as a raw material for production of fused magnesium oxide.
Specific gravity: 2.9-3.1
Hardness: 3.5-4.5 Mohs
Properties
Surface Modifier - Matte
In low temperature glazes magnesium carbonate in amounts to 15% acts as a refractory, remaining in suspension in the glaze melt to produce a white opaque matte glaze.
Surface Modifier - Crawling
Magnesium carbonate is commonly added to glazes, especially at low fire, to make them crawl (it shrinks and cracks the glaze layer at the low end of firing and then its high melt viscosity pulls the glaze melt into islands). This often produces dramatic visual effects, especially if the crawling glaze color contrasts with the underlying body or slip. Additions vary from 10-30% depending on the host glaze.
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
XML
<?xml version="1.0" encoding="UTF-8"?>
<material name="Magnesium Carbonate" descrip="MgCO3, Magnesite" generic="1" rawmineral="0" searchkey="Mag Carb" loi="56.50">
<families>
<family name="Flux Source"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="" percent="0.500" tolerance=""/>
<oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="" percent="43.000" tolerance=""/>
<oxide symbol="SrO" name="Strontium Oxide, Strontia" status="" percent="0.250" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="0.150" tolerance=""/>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="0.040" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="56.500" tolerance=""/>
</volatiles>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>See also Light Magnesium Carbonate.
Magnesite is used in pottery bodies, glazes, and glass. It is quarried in California, Washington, Austria, Russia, Manchuria, Greece and Slovakia and processed from sea water. Sources are reasonably consistent in the CO2 content, but can vary widely in the iron and significantly in the MgO.
Magnesite decomposes at 900C, losing its carbon dioxide.
Heavy and light varieties are available. Light magnesium carbonate or hydromagnesite is made by boiling together solutions of magnesium sulfate and sodium carbonate. Light magnesium carbonate is used as a electrolyte in both ground and cover coat enamels. It is added (.12-.25%) to flocculate clay slurries, improving and stabilizing the set and suspension characteristics.
Magnesium carbonate by itself is very refractory, and is used to make bricks for the cement and metal industries. It is \'dead burned\' in rotary kilns, then reground, sized, and dry pressed using organic binders.
Magnesite is used in low fire glazes in to produce opacity and matteness.
Dolomite and talc are more practical sources of MgO for most higher temperature applications.
In glaze melts it is an active flux at higher temperatures (2150C+), and it produces elasticity, a lower expansion coefficient and smooth buttery surfaces. At lower temperatures it is a refractory and will matte glazes and make them crawl due to its high shrinkage and contributions to the suface tension of the melt.
Magnesite is also as a raw material for production of fused magnesium oxide.
Specific gravity: 2.9-3.1
Hardness: 3.5-4.5 Mohs</note>
</notes>
</material>
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