Part of the fossil record, stromatolites belong to what rock group and are formed when minerals are precipitated out of water by prokaryotes in a microbial mat?
crystalline
metamorphic
igneous
sedimentary
Stromatolites Fossilized microbial mats represent the earliest record of life on Earth. A stromatolite is a sedimentary structure formed when minerals are precipitated out of water by prokaryotes in a microbial mat (Figure 22.3). Stromatolites form layered rocks made of carbonate or silicate. Although most stromatolites are artifacts from the past, there are places on Earth where stromatolites are still forming. For example, growing stromatolites have been found in the Anza-Borrego Desert State Park in San Diego County, California.