place via pressure solution. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. Mechanical compaction takes place primarily at depths less than . Chemical compaction continues to depths of , and most cementation takes place at depths of . Unroofing of buried sandstone is accompanied by telogenesis, the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the sandstone, such as dissolution of some of the cement to produce secondary porosity. Components Framework grains Framework grains are sand-sized ( diameter) detrital fragments that make up the bulk of a sandstone. Most framework grains are composed of quartz or feldspar, which are the common minerals most resistant minerals to weathering processes at the Earth's surface, as seen in the Goldich dissolution series. Framework grains can be classified into several different categories based on their mineral composition: Quartz framework grains are the dominant minerals in most clastic sedimentary rocks; this is because they have exceptional physical properties, such as hardness and chemical stability. These physical properties allow the quartz grains to survive multiple recycling events, while also allowing the grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in origin and also from older sandstones that have been recycled. Feldspathic framework grains are commonly the second most abundant mineral in sandstones. Feldspar can be divided into alkali feldspars and plagioclase feldspars, which can be distinguished under a petrographic microscope. Alkali feldspar range in chemical composition from KAlSi3O8 to NaAlSi3O8. Plagioclase feldspar range in composition from NaAlSi3O8 to CaAl2Si2O8. Lithic framework grains (also called lithic fragments or lithic clasts) are pieces of ancient source rock that have yet to weather away to individual mineral grains. Lithic fragments can be any fine-grained or coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments found in sedimentary rocks are clasts of volcanic rocks. Accessory minerals are all other mineral grains in a sandstone.