The major difference between shale and sandstone is the type of materials from which they are formed and the size of the particles. Shale is made primarily from clay and has a much finer grain that sandstone. Sandstone is made primarily of sand and has a larger grain.
Both sandstone and shale are sedimentary rocks, and they are both from the same basic type known as clastic sedimentary rocks. This type of rock is formed from the weathering of debris and not from any chemical reactions. Both shale and sandstone are common types of rocks, and both have about the same density. Shale is a laminated rock, which means that it is comprised of thin layers. Because shale is prone to split apart at the layers, shale is also fissile. Shale is formed when silt and clay-sized minerals compact together over time. Slate must be composed of at least 67 percent clay. The remaining part of shale includes larger particles of silt or gravel, minerals and organic matter. Sandstone is made of sand-sized mineral particles, most often sand itself. Along with the sand, there is a material in the sediment known as the matrix and also an additional material that holds all the grains together.