Plane polarised light

Thin section of a fused siltstone/mudstone known as buchite within a sill. Partial melting has enabled the growth of various high temperature minerals including sapphires, an aluminium silicate and a variety of corundum. Their pale blue colour is just discernible, especially towards the top centre.

Cross polarised light

The above photo in xpl illustrates the high birefringence of corundum (sapphires). Their interference colours include purple, yellow and red. The minerals showing grey interference colours are feldspars.

Plane polarised light, highly magnified, showing a possible mullite (aluminium silicate) needle towards bottom left and ?crystallites forming within the fused mudstone towards centre right.

Back to thumbnails.

 Map showing locality of Rubh a' Chromain, Carsaig Bay, Mull, NM526 203

The Created with Memory-Map. ©Crown Copyright. Licence number 100034184. www.memory-map.co.uk
Geological Conservation Review (GCR) quotes the Rubh' a'Chromain composite xenolithic sill as belonging to the Scridain Suite of sills, its significant feature being the distinctive, high-temperature mineralogy of the thermally metamorphosed aluminous xenoliths.