Sandstone and siltstone are both sedimentary rocks, but they differ in their grain size and composition.
Grain Size
Sandstone is composed of sand-sized grains, which are larger than the silt-sized grains found in siltstone. The grains in sandstone typically range from 0.0625 mm to 2 mm in diameter, while siltstone grains are smaller, ranging from 0.0039 mm to 0.0625 mm.
Composition
Sandstone is primarily made up of quartz or feldspar, which are the most common minerals found in sand. Siltstone, on the other hand, is composed mainly of silt-sized particles, which can include quartz, feldspar, and clay minerals.
Texture
Sandstone has a gritty texture due to its larger grains, whereas siltstone has a smoother, finer texture because of its smaller grains.
Formation
Both rocks form from the accumulation and compaction of sediment. Sandstone forms in environments like beaches, deserts, and riverbeds where sand is deposited. Siltstone forms in quieter environments like lakes, lagoons, and deep ocean basins where fine silt settles.
In summary, the main differences between sandstone and siltstone are their grain size, composition, and texture. Sandstone has larger grains and a grittier texture, while siltstone has finer grains and a smoother texture.