Why are sedimentary frocks more porous than motamorphic or igneous rocks?
All down to the formation of the rock types. Igneous are created by the cooling of magma, either within the earth itself (Intrusive) or as it erupts out of the ground (Extrusive). This cools to form vaious hard rocks such as Granite. The speed of cooling dictates what type of rock it becomes. Metamorphic rocks are formed when one type of rock is put under great strain/pressure and/or heat. So limestone put under great heat, as when an extrusion of magma pushes through its layers, will be matamorphosed into marble. Mudstone will become slate and so on. Both of these types are all created through intense pressure and heat, which squeezes out all of the space between the individual mineral particles and so there is little to no room for water to pass through. Sedimentary rocks on the other had are exactley that: layers of sediment layed down through either the action of water or wind. As the layers build the pressure pushes the layers tighter together to form a rock, but the molecules do
Sedimentary rocks are as most have suggested made by the accretion of small separate particles, fine =mud becomes mud stone, silt becomes siltstone, sand, sandstone etc. The particals retain their original shape and as in a hand full of beach sand, there are spaces or pores in between them. The particals are sometimes cemented together chemically (similar to concrete), but this can still leave pores, or sometimes just enough heat and pressure is around to force the particals to stick together permanently. Still thise spaces. In fact it is onlt called sedimentary rock if you can still identify the original particals. Some exceptions to the above, are lime stones, chalk and other chemical sedimentary rocks formed fom disolved minerals precipitaiting out from solution. These generally do not have any pores. They may havelots of cracks etc though. Igneous rocks are made from molten magma. If cooled deep in the ground you get large crystal rocks with no pores. If cooled closer to the surfac
The difference is the condition in which they are formed. Igneous rocks are formed when magma solidifies. Since the magma is in a liquid-like state, it fills the area it occupies, thus filling in pores. Metamorphic rocks are formed deep within the earth via extreme heat and pressure. The pressure compacts the rocks so much that pores are rarely present. Sedimentary rocks are formed mainly by the accumulation of sediments or precipitates from a solution. Since these rocks are formed by many smaller pieces being pressed together by much less temperature and pressure than the other two types, it makes for a less dense, looser material which enables pores to remain.
