Magnesium carbonate as a fill material for marble

I am analyzing a repair (fill material) from a marble sculpture
(believed to be sculpture grade Carrara marble). Analysis (by FTIR
and XRD) showed the fill material to be composed of a hydrated
magnesium carbonate with a smaller amount of quartz and probably
sepiolite (a magnesium silicate). No organic binder was detected.
I'm wondering if this could be a type of plaster fill based on
magnesium carbonate rather than calcium carbonate.

I have found reference to the presence of  magnesium carbonates in
plasters where the lime comes from a magnesium-rich limestone,
however I have not found any reference to plasters where hydrated
magnesium carbonate is the major component. Has anyone come across
this type of fill or a reference to the use of magnesium carbonate
based plaster?

Kate Helwig
Conservation Scientist
Canadian Conservation Institute
Ottawa, Canada


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                  Conservation DistList Instance 15:56
                Distributed: Thursday, February 14, 2002
                       Message Id: cdl-15-56-015
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