a laminated, sedimentary rock structure formed primarily in Precambrian shallow pools by mats of sticky, blue-green algae, which trapped layers of silt, esp. of calcium carbonate: these wavy or round formations serve as evidence for dating the first life forms on earth and are still being produced today
See stromatolite in American Heritage Dictionary 4
A widely distributed sedimentary structure consisting of laminated carbonate or silicate rocks, produced over geologic time by the trapping, binding, or precipitating of sediment by groups of microorganisms, primarily cyanobacteria.
Origin: Late Latin strōma, strōmat-, covering; see stroma