First Thin Sections of Experimentally Melted Igneous Rocks: Sorby's Observations on Magma Crystallization

Abstract

The first thin sections of artificially melted rocks were made in 1862 by Henry Sorby from specimens of Sir James Hall's experimentally fused basalts and of a fused granodiorite. Sorby's work on the fused basalts showed that the cooled charges contained the same three phases, although texturally different, as the starting materials and thus vindicated Hall's experiments. Sorby's observations on the granodiorite reinforced his earlier conclusions, based on fluid inclusion studies, that water plays a major role in plutonic crystallization. It is here suggested that Sorby's work on fused rocks in the period 1860-1863 was a response to a challenge from Alexander Bryson to prove that granite is of igneous origin.