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)