Greywacke sandstone is a type of sedimentary rock characterized by its dark color, typically grey or greenish-grey, and a coarse texture. It is composed mainly of quartz, feldspar, and rock fragments, often embedded in a finer matrix of clay or silt. This rock forms in marine environments, particularly in areas with strong currents, which help in the mixing of sediments. Greywacke is known for its durability and is often used in construction. Its unique composition and formation process make it a significant indicator of past geological conditions, providing insights into ancient environments and tectonic activities.