CLASTIC SEDIENTARI ROCKS

Clastic rocks are made up of particles of pre-existing rocks and minerals. These particles may have originally been from igneous rocks, metamorphic rocks, or even other sedimentary rocks. Clastic rocks are deposited under the influence of some type of current (flowing water, waves, winds, or moving ice), therefore particle size is a reflection of the amount of energy that transported the sediments to the place of deposition and tells us something about how the rock was formed.
Particle size is described in three major categories, gravel (all particles larger than 2 mm in diameter), sand (particles smaller than 2 mm, but larger than 0.0625 mm), and mud (particles smaller than 0.0625 mm). The first step in any identification of a clastic rock is to determine the grain size of the particles. If more than 30% of a rock is composed of gravel sized clasts, then it is either a conglomerate or a breccia. A conglomerate has clasts which have rounded corners, a breccia has clasts with angular corners. Remember, the shape of the grains in the rock is the important feature, not the shape of the hand specimen.
All clastic rocks which are made up of sand sized particles are called sandstones, but not all sandstones are alike. The three common types of sand particles are quartz, feldspars and rock fragments. If the sandstone is made up mostly of quartz, it is called a quartz sandstone. If the sandstone have a significant amount of feldspar grains, it is called an arkosic sandstone. In order to differentiate between a quartz sandstone and an arkosic sandstone, you must be able to tell the difference between quartz and feldspar. Arkosic sandstones have a high percentage of quartz, but also contain identifiable feldspar grains. The final type of sandstone is made up of rock fragments. These may be pieces of basalt, shale, limestone, rhyolite or even other sandstone, and the rock is called a lithic sandstone or litharenite.
Clastic rocks made up of mud sized particles have particles too small to see either shape of composition, so classification is based on the properties of the rock as a whole (rather than the grains), or by particle size. Mud includes two subgroups, the coarser grains are silt (0.0625 mm to 0.0039 mm) and the finer grains are called clay (smaller than 0.0039 mm in diameter). A rock dominated by silt particles is called a siltstone. A rock dominated by clay particles is called a claystone. By now you are asking yourself, if the particles are too small to identify, how can I tell them apart. Your eyes are less sensitive than your touch. Sand will feel gritty between your fingers, but silt will feel smooth. Clay particles are so small that the particles even feel smooth on your teeth (a test which must be performed to be believed). Most rocks in the mud family are made up a mixture of silt and clay sized particles. In these cases, if the rock shows some degree of bedding (layering caused by gravity) then the rock is called a shale. If the rock shows no evidence of bedding (described as massive) it is called a mudstone.