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
California Coastal Comm'n v. Granite Rock Co. The Coastal Commission did not seek to prohibit mining of the unpatented claim, only to regulate mining activity in accordance with the detailed requirements of the California Coastal Act. Granite Rock filed an action in U.S. District Court claiming that the Coastal Commission permit requirement was preempted by Forest Service regulations, by the Mining Act of 1872, and by the Coastal Zone Management Act. The District Court denied Granite Rock's motion for summary judgment, and dismissed the action. The Court of Appeals for the Ninth Circuit reversed the lower court's decision, holding that the Coastal Commission permit requirement was preempted