Stromatolite: Microbial mat; This slab measures 15” (38.1 cm.) long, 15” wide (38.1 cm.), and 5/8” (1.5 cm.) thick. It has beautiful color and exceptional detail. The mat is formed as follows: On an ancient beach, billions of prehistoric micro-organisms formed a living colony, creating a thin and interwoven fiberous mat. This stromatolite mat formed quickly, between the tides, and was held together by a glue-like substance secreted from the living eco-system. The fiberous mat not only preserved the ripple marks in the fine-grained beach sand, it also created its own unique “footprint” among those ripples.