Gneiss

Gneiss (pronounced "nice") is a coarse-grained regional metamorphic rock. Heat as well as pressure is involved in its formation. It is about as metamorphosed as a rock can be. Often it is impossible to tell what the original rock was. As a rule the mineral content of gneiss is similar to that of a very high-grade schist. The minerals, however, are much coarser and separated out into distinct bands.

These excellent samples of gneiss are "Kennack Gneiss" (only found on Kennack Sands, The Lizard, Cornwall). It forms as part of the Lizard Ophiolite Complex.

It consists of interlayered bands of pale granite and dark basalt - strange geological bedfellows. How come they're in bed together? Possibly this is because as Gondwana piled slices of the Rheic Ocean on to the Lizard, deeply buried mica and hornblemde schists started to melt, forming light and dark bands - a geological proces known as anatexis. More probably, as the Lizard rocks were bulldozed northwards, separate granitic and basaltic melts were fused together and injected like striped toothpaste between the Lizard rock slices.
"Beneath The Skin Of The Lizard", Robin Bates and Bill Scolding

The Lizard Ophiolite Complex