Two contrasting granite types: 25 years later

The concept of I- and S-type granites was introduced in 1974 to account for the observation that, apart from the most felsic, rocks, the granites in the Lachlan Fold Belt have properties that generally fall into two distinct groups. This has been interpreted to result from derivation by partial melting of two kinds of source rocks, namely sedimentary and older igneous rocks. The original publication on these two granite types is reprinted and reviewed in the light of 25 years of continuing study into these granites.