Is gravel igneous, sedimentary or metamorphic rock?
The term ‘gravel’ has two senses. As a natural component of sedimentary deposits, it refers to material coarser than sand; the cutoff being about 4 mm diameter. In this sense, the description is limited to naturally occurring particles, either in a loose deposit, or as grains in a sedimentary rock. ‘Gravel’ is also commonly used to describe any coarse rock material; including crushed gravel, made by crushing hard rock (technically, a more correct term in this case would be ‘crushed aggregate’; used in concrete and road building). Natural gravel, by its nature (being the end product of erosion, transport and deposition) is more likely to be composed of the harder rock types. Sandstone, for instance does not often form extensive gravel beds; because it is usually eroded down to sand; which makes up the grains within the rock. Limestone does not form gravel beds very frequently either; unless they are close to the source rock. Older gravel beds are more likely to be composed of harder ign
