Dolomite is CaMgCO3 where some or all of the calcium is substituted by magnesium, and is sometimes called dolomitised limestone. Magnesium does not react with HCl, therefore HCl is always used as an indicator for calcium carbonate whether calcite or aragonite.
The marble are basically two type calcitic (calcium carbonate) with other minerals. While dolomitic when in chemical composition you find magnesium along with calcium carbonate and the % of magnesium is reaching upto 18 to 20%,, the calcitic marble chemical composition is caco3 while dolomitic chemical composition is camgco3(calcium magnesum carbonate....................anwar consultant geologist