Definition: Umbrine is a type of sedimentary rock that forms from the accumulation and precipitation of organic material. It is often found in mountain ranges, rivers, lakes, and other bodies of water where it can be found in various forms such as sandstones, siltstones, claystones, or shales. Umbrines are characterized by their distinctive red coloration due to the presence of iron oxides that form when organic material decomposes. They are often associated with sedimentary deposits and can