Geology of Alderney

Although Alderney is only five kilometers long, it has a geological history spanning half of the life of the earth.

However the earliest dated rock is the grey coloured Western Granodiorite from 2,220 million years ago in the Paleoproterozoic.

The next stage of geological history was the intrusion of the Central Diorite Complex that makes up the north and centre of the island.

Embedded in the diorite are a couple of large gabbro inclusions, as well as a picrite on the east of Braye Bay.

Some of the diorite has orbicular structure, concentric spheres of plagioclase and hornblende rich zones form balls up to 20 cm in diameter.

As in Jersey, loess blew in as dust from the bare ground in the near glacial conditions in the ice ages.