Human: I'm trying to find out about different types of sandstone. Assistant: 
Sandstone is a sedimentary rock composed of sand-sized grains that are cemented together by silica or other minerals. It can be classified into two main categories, quartzose and feldspar-rich sandstone, based on the composition of its grains. Quartzose sandstone contains more than 50% quartz and has a higher resistance to weathering and erosion. Feldspar-rich sandstone has less than 50% quartz and is more easily weathered and eroded.