pitchstone inselberg sgurr geology

Pitchstone monadnock

pitchstone mountain sgurr volcanic glassA spectacular pitchstone ridge on the Isle of Eigg Scotland, rises out of the surrounding small islands landscape.

Sgurr, which means The Notch, has sheer cliffs and is 400 meters (1300 feet) high.

The island mountain Sgurr of Eigg in geology is known as a monadnock in the USA, inselberg in Europe or a koppie in Africa. These are lonely mountains, hills or buttes with different rock to the local area they rise up from.

Pitchstone An Sgurr

pitchstone sgurr koppie butte
An Sgurr of Eigg is made of pitchstone which is a rarer variation of volcanic glass rock. How was this stand out pitchstone monadnock formed?

An Sgurr was formed as lava poured though a prehistoric riverbed from a volcano on the neighbouring island Rum. Over millions of years, the surrounding land has eroded, leaving the harder pitchstone ridge behind.
An Sgurr (The Notch) | Isle of Eigg

pitchstone locations isle of eigg scotland

Pitchstone volcano glass rock is famous for its high water content that makes it appearance much duller than obsidian.

For a valley mould of Sgùrr size on a small island how would a stream have enough volume of water while lava pouring out? Eigg is only 5 miles by 3 miles.

How would a stream keep flowing into and through the lava to create pitchstone up to 200 meters thick?

The pitchstone mountain also has similar hexagonal columns to the Giants Causeway in Northern Ireland.

Pitchstone Butte

pitchstone isle of sgurr
The Isle of Eigg’s Sgurr has a similar shape to buttes and Qollas seen around the world, with one end having a ridge leading up to it with a triangular shape.