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 Island (Michigan) Granite Island (Michigan) Granite Island is a island in Lake Superior located about northwest of Marquette in the Upper Peninsula of the U.S. state of Michigan. Built upon it is the Granite Island Lighthouse, also known as Granite Island Light Station, "one of the oldest surviving lighthouses on Lake Superior". It is part of Marquette Township, in Marquette County. The island is granite rock that rises nearly perpendicularly to above the surface of Lake Superior, surrounded by deep water. The Native Americans called the island "Na-Be-Quon". That apparently meant something like 'vessel'. They called a steam ship an "ishcoda nabequon".