A mud stone pic. Sediment from flowing water lays down layers, the mud/sand dries quickly when the flood recedes, forming cracks, then is buried again. Millions of years later, you find the pieces eroding out. Maybe.
Sandstone is a type of sedimentary rock. It forms when grains of sand are compacted together over very long periods of time. Normally this sand has an abundance of quartz but can also contain other minerals and materials. A small proportion of other mineral grains such as feldspar, mica, and rock fragments may also be present. The grains may be closely packed together forming a compact stone or sparsely distributed to form a porous stone. While sand is the most common element found in sandstone, there can often be other materials found in it such as cement and matrix. Cement located within the stone is usually comprised of quartz, calcium carbonate or iron oxide. Sandstone comes in a variety of colours including red, yellow, gray, and brown.