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
What Is Life what he needs from his old band – that insinuating hook sense – and uses it to frame an utterly comfortable metaphysical discourse". Alan Clayson describes "What Is Life" as a seemingly "lovey-dovey pop song" that "craftily renewed the simplistic tonic-to-dominant riff cliché", while Simon Leng credits Harrison's "innate ability to write very fine pop-rock songs" and deems the result "as innovative an exercise in rock-soul as The Temptations' 'Cloud Nine'". Among Harrison biographers, only Ian Inglis is less than enthusiastic, acknowledging that Barham's orchestration and the other musicians give the track "undoubted excitement and energy", but lamenting that the