Sedimentary rocks are those rocks made up of pieces of other rocks. We call the pieces of rock "clasts" (Clast means "broken piece"). A clast is a piece of rock broken off of another rock. Clasts of rock are eroded from larger rocks, transported (moved) by wind or water and deposited in a basin.After some period of time, the clasts are lithified (lithos is the Greek word for stone). The sedimentary rocks we see today were once gravel, sand, silt, mud, or living things. We decide what to name sedimentary rocks based on the size of the clasts that make up the rock. For most sedimentary rocks, this is easy. Sandstone is made of sand, siltstone is made of silt, mudstone is made of mud and so on. Even volcanic ash can become sedimentary rock! The only hard ones to remember are conglomerate and breccia. Conglomerates are made up of rounded, gravel-size particles (To a geologist, gravel is anything from 2mm to 4 meters in diameter), and breccia is made up of angular, sharp-edged, gravel-sized clasts. Limestone and chert are classified as sedimentary rocks, but most limestone and chert are grown by living organisms rather than broken from other rocks. Some limestones have fossils, but most limestones and cherts have recrystallized, and the remains of the creatures that made them are no longer visible.