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
Granite Rock Township, Redwood County, Minnesota Granite Rock Township, Redwood County, Minnesota Granite Rock Township is one of the twenty-six townships of Redwood County, Minnesota, United States. The population was 241 at the 2000 census. Granite Rock Township was organized in 1890, and named for the granite rock formations in the Redwood River valley. According to the United States Census Bureau, the township has a total area of ; of it is land and of it (0.05%) is water. Per its name, Granite Rock Township contains deposits of granite, a rock composed of three different major minerals. The city of Lucan is located in Granite Rock