Sedimentary rocks are not made from grains of "grains" in the sense of cereal grains like wheat, rice, or corn. Instead, they are made from sediments, which are small pieces of other rocks, minerals, and organic materials that have been broken down by weathering and erosion.

Here are some common types of sediments that make up sedimentary rocks:

* Quartz: A hard and resistant mineral, commonly found in sandstone.

* Feldspar: Another common mineral found in sandstone, but less resistant to weathering than quartz.

* Clay minerals: Tiny, platy minerals that form from the breakdown of other rocks. They are common in shale and mudstone.

* Calcite: A carbonate mineral that forms shells and skeletons of marine organisms. It's the main component of limestone.

* Rock fragments: Broken pieces of other rocks, such as pebbles, sand, or gravel. These are common in conglomerate and breccia.

* Organic matter: The remains of plants and animals, like fossilized shells, leaves, or wood. These contribute to the formation of coal and oil shale.

So, while we might use the word "grain" to describe the individual particles that make up a sedimentary rock, it's important to remember that these "grains" are not the same as the cereal grains we eat.