Cordierite in the Skiddaw metamorphic aureole

Amongst the rocks at the Roughten Gill bridge, you find these spotted stones.

I have learned a new word. I knew that the hornfels in which the cordierite appears is metamorphosed mudstone but the term for metamorphosed mudstones is PELITE. The crystal structure is interesting. It is made  up of a lattice of magnesium or iron atoms, then oxygen and then silicon and aluminium. There is a picture of the structure here https://en.wikipedia.org/wiki/Cordierite It would be good to link that with the stuff I've been learning about crystal structure in solid state physics. I was also interested that synthetic cordierite is used in catalytic converters.

Cordierite is