Gneiss

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It's very nice.

a bit more here about what it's like to climb on

Geology

Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.

Gneissic rocks are usually medium- to coarse-foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. Depending on their composition, they may also be called garnet gneiss, biotite gneiss, albite gneiss, etc. Gneiss displays compositional banding where the minerals are arranged into bands of more mafic minerals and more felsic minerals. This is developed under high temperature and pressure conditions.

Lewisian

Most of the Outer Hebrides of Scotland have a bedrock formed from Lewisian gneiss. These are the oldest rocks in Europe and amongst the oldest in the world, having been laid down in the Precambrian period, up to 3000 million years ago. In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree. These rocks are largely igneous in origin, mixed with metamorphosed marble, quartzite and mica-schist and intruded by later basaltic dykes and granite magma. The gneiss's delicate pink colours are exposed throughout the islands.

Where to Climb Gneiss Rock in Scotland

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