Magnesium carbonate light

white very light-weight powder (and bag of this material is like a bag of feathers). It is practically insoluble in water. This is not the same material as magnesium carbonate (magnesite).

This material is very refractory, it does not decompose and give up its MgO to the glaze melt easily. Magnesium carbonate is a good example of the need to consider mineralogy and material level physics in addition to chemical makeup when using ceramic chemistry to adjust and fix glazes. Two glazes may have the same calculated chemistry, but the one using the mag carg to source the MgO will not be melted as much.