Granite may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase. It is on this basis that the modern "alphabet" classification schemes are based. The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources). Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks. M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from the mantle. However, this proposal has been rejected by
Bohus granite the time of the formation of the Sub-Cambrian peneplain in the Late Neoproterozoic the rocks were at surface. Subsequently, the granites were buried in sediments and then intruded by NNW-SSE oriented basic dykes in the Permian. In the Mesozoic the rocks were subject to significant weathering resulting in the formation an irregular grand-scale relief called the Sub-Mesozoic hilly peneplain. At a smaller scale the weathering is thought to have produced numerous small rock basins now seen near the coast. Bohus granite The Bohus granite () is a type of granite that crops out along the Swedish West Coast in Bohuslän.