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
Wave Rock land surface. This process formed underground "domes" of solid granite bedrock surrounded by deeply weathered, relatively loose, and disaggregated granite. Following separation of Australia and Antarctica and accompanying tilting of what became southwestern Australia, periodic erosion of the deeply weathered granite, which underlaid the surrounding land surface, exposed these buried solid bedrock domes over time as Hyden Rock. Wave Rock is a spectacular example of what geomorphologists call a "flared slope". A flared slope is a concave-upward or -inward bedrock surface that is typically found around the base of inselbergs, bornhardts, and granitic boulders and also on their higher slopes.