Common stromatolitic rock types
are: dolostone as well as limestone, the dolostone forming diagenetically
or syngenetically in evaporitic in evaporitic regions. Another common
rock type where fossil stomatolites are found is chert, which unlike carbonates,
only make up a portion of the stromatolite, with the remainder being a
carbonate rock. 
Generally chert-stromatolites occur in the pre-phanerozic, where the deposition of this material was more prominent.
It is thought that the silicate materials replaced
the carbonate during diagenesis of the sedimentary body. There have
also been discoveries of phasphatic stromatolites, also thought to have
occur during diagenisis.
Left: Stromatolite in Mary
Ellen Jasper, Minn., 2.1 BA (www.academic.emporia.edu)
Right: Stromatolite fossil
in Kaona Dolomite, Michigan, 2.2 BA (www.academic.emporia.edu)
