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
Exfoliating granite president of the Geographic Society to receive the highest honor for geographic accomplishment; Hubbard Medal. Working his way down the Great Basin, Gilbert knew the general formation of mountains through a tectonic process, and are composed of different rock types. He observed that the mountain ranges in this area contained similarities in strata, resembling bubbles and blisters on the earth’s surface. He concluded that the mountains were once intrusive magma that had and became visible with erosion. Gilbert presented his findings in a report and contributed significantly in what future generations would know as Geomorphology. Exfoliating granite Exfoliating granite is