#ThinSectionThursday Here's one of my favourite rocks of all time, from Kilfinichen Bay, Mull - a melted shale xenolith in one of the Loch Scridain Sill suite of intrusions. It contains giant pink-colourless (blue-purple) mullite crystals, with small squarer colourless (grey-white) cordierite crystals, enclosed in dark, feathery-textured quenched melt. Field of view about 2mm wide - more info in the Alt text of the images. #Geology #Microscopy #SanidiniteFacies #ExperimentalPetrology