The commonest lamprophyres are associated with large masses of granite and diorite. Classic examples occur in the Highlands and southern uplands of Scotland, the Lake District of Ireland, the Vosges, the Black Forest, and the Harz Mountains. Lamprophyres show a strong tendency to weather and decompose.

How is a Lamprophyre formed?

Distribution. Lamprophyres are usually associated with voluminous granodiorite intrusive episodes. They occur as marginal facies to some granites, though usually as dikes and sills marginal to and crosscutting the granites and diorites. In other districts where granites are abundant no rocks of this class are known.

How is granodiorite formed?

Granodiorite is a plutonic igneous rock, formed by intrusion of silica-rich magma, which cools in batholiths or stocks below the Earth's surface. It is usually only exposed at the surface after uplift and erosion have occurred.