The structure of different sand and gravel varies greatly, some particles are coarse and uniform, some are of different sizes; some gravels have well rounded debris in the sand and gravel, some have sharp angles. Sandstone is a loose material, but its particles are generally hard and chemically stable under the surface environment. For sandstone gravel is often widely used in houses, roads, highways, railroads, engineering and other fields as a high-quality construction material and concrete raw material because of its good hardness and stable chemical properties. Come to say, its resistance to weathering is generally strong, especially the silicified quartz sandstone, whose hardness exceeds that of granite.