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
Barre granite Barre granite Barre granite /ˈbæri/ is a Devonian granite pluton near the town of Barre in Washington County, Vermont. Richardson described it as a "fine granite, composed of quartz, feldspar, and mica. The mica is both muscovite and biotite." It intrudes into the Waits River Formation. The granite is mined at the E. L. Smith Quarry, owned by the Rock of Ages Corporation. "Barre Gray" granite is sought after worldwide for its fine grain, even texture, and superior weather resistance. Many sculpture artists prefer it for outdoor sculpture. Sculptor Frank Gaylord used it for the United States Korean War Memorial