Fig. 3.

All images crossed polarised light. a Quartz–biotite–hornblende monzonite from Ben Nevis, Scotland (sample 14105 from the Harker Collection, University of Cambridge), showing well-preserved euhedral plagioclase grains with random orientation, with interstitial quartz. b Higher magnification view of a showing the shape of an interstitial quartz grain. The geometry of the pore corners is dominated by the impingement of the plagioclase grains, with slight modifications that are probably due to simultaneous growth of feldspar and quartz during the late stages of solidification. c Granite from Marsco, Skye (Scottish Inner Hebrides), showing a fine network of cuspate feldspar grains interstitial to rounded grains of quartz. Such features indicate relatively early crystallisation of quartz, followed by nucleation and growth of feldspar in a system that was approaching melt–solid textural equilibrium. Sample 124523 from the Harker Collection, University of Cambridge. d Close-up of an area of c, showing the complex intergrowth of feldspar and quartz. Note the low dihedral angles and the cuspate shape of the minor feldspar component, which suggests pseudomorphing of originally texturally equilibrated melt-filled pores between the rounded grains of quartz. e Granite from Virolahti, South Finland. Sample 87817 from the Harker Collection, University of Cambridge. f Higher magnification view of e, showing cuspate interstitial feldspar grains (Pl and Kfs, arrowed) that preserve a low feldspar–quartz–quartz dihedral angle. This is consistent with the feldspar having pseudomorphed a previously melt-filled pore space, close to hypersolidus textural equilibrium. g Granite from Coire Lan, Arran, Scotland, showing an irregular film of quartz (Qz, arrowed) separating alkali-feldspar grains (Kfs). Such a feature suggests that quartz infilled a grain-boundary melt film with irregular margins. h Hornblende granite, Skye (Scottish Inner Hebrides), dominated by granophyric intergrowths that nucleated on and grew away from earlier crystallised euhedral grains of plagioclase