The recrystallization that takes place does so essentially in the solid state, rather than by complete remelting, and can be aided by ductile deformation and the presence of interstitial fluids such as water.Metamorphism often produces apparent layering, or banding, because of the segregation of minerals into separate bands.Rocks are commonly divided into three major classes according to the processes that resulted in their formation.
That is to say, porosity is the ratio of void volume to the bulk volume (grains plus void space).
They originate from processes deep within the Earth—typically at depths of about 50 to 200 kilometres (30 to 120 miles)—in the mid- to lower-crust or in the upper mantle.
Igneous rocks are subdivided into two categories: Sedimentary rocks are those that are deposited and lithified (compacted and cemented together) at the Earth’s surface, with the assistance of running water, wind, ice, or living organisms.
Thus the total porosity (ϕ, the total porosity is Apparent (effective, or net) porosity is the proportion of void space that excludes the sealed-off pores.
It thus measures the pore volume that is effectively interconnected and accessible to the surface of the sample, which is important when considering the storage and movement of subsurface fluids such as petroleum, groundwater, or contaminated fluids.
These three classes, in turn, are subdivided into numerous groups and types on the basis of various factors, the most important of which are chemical, mineralogical, and textural attributes.