Ken:

Some limestones have significant iron, especially those with some dolomite
content.  Some may have layers or nodules of siderite or ankerite which are
types of iron carbonate (limestone is dominantly calcium carbonate). These
may weather (decompose by exposure to water, acid, etc.) to various other
iron compounds (hematite, goethite, jarosite, etc.) which have yellowish,
brown, or red coloration.   Don't know about the specific limestones you
have from Indiana (there are many).  This staining can be cleaned from some
rocks by soaking in warm oxalic acid (a fairly benign substance), but I
don't know if this is possible, or even safe, in your situation, or even if
it may further damage the building stones.  Different joints may show
stains while others don't because they may have cut irregularly through the
iron-rich layers or segregations in the quarry when shaping the stones, and
some blocks may have these compounds exposed in joints while others are
protected by less iron-rich limestone surrounding it.
--
Tim "Laura's Geologist/Nerd Husband" Demko



>Is there iron in limestone?
>Is there iron in Indiana limestone?
>When repointing limestone why might some joints show an orange stain when
>similar joints show no staining?
>
>Thanks,
>][<en Follett


--
Laura Demko
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