The grains in a sandstone can be composed of mineral, rock, or organic materials. Which and in what percentage depends upon their source and how they were altered during transport.

Mineral grains in sandstones are usually quartz. Sometimes the quartz content of these sands can be very high – up to 90% or more. These are sands that have been worked and reworked by wind or water and are said to be “mature.” Other sands can contain significant amounts of feldspar, and if they came from a source rock with a significant quartz content, they are said to be “immature.”