Figure 3
From: A large explosive silicic eruption in the British Palaeogene Igneous Province
Comparison of textures in single crystal and crystal clots in the Òigh-sgeir and Sgùrr of Eigg pitchstones. (a) Microphotograph of Òigh-sgeir pitchstone with resorbed feldspar and small pyroxene grains in glassy matrix (CPL). (b) Òigh-sgeir pitchstone with large resorbed feldspar crystal (PPL). (c) Large (sieve-textured) and resorbed feldspar crystals in glassy Òigh-sgeir pitchstone. Note the outer edge (top side of the crystal) is intact, while resorption appears to have attacked the feldspar “internally” (PPL). This ‘internal’ resorption features in the K-feldspar and Na-feldspars suggest that heating was the main agent for resorption75. (d) Representative plutonic inclusion (plagioclase, pyroxene, opaques) in Òigh-sgeir pitchstone (CPL). Note the resorbed feldspar in the inclusions. (e) Small plagioclase cluster in Sgùrr of Eigg pitchstone (CPL). Note the resorption of the feldspars. (f) Base of Sgùrr of Eigg pitchstone. Note the mafic schlieren (‘fiamme’) in top part of image (above resorbed feldspar), indicating mafic magma was present during the eruption (PPL). (g) Photomicrograph of sieve-textured feldspar fragment in Sgùrr of Eigg pitchstone with intact outer edge (upper side), set in a glassy groundmass (PPL). (h) Photomicrograph of upper Sgùrr of Eigg deposit with a plutonic inclusion that comprises resorbed feldspar, pyroxene and opaques. Most of the feldspars show evidence of initial to advanced resorption. Importantly, the Sgùrr of Eigg and Òigh-sgeir pitchstones are strikingly similar, displaying the same mineral-types, mineral assemblage and identical mineral textures.
