Garnet pyroxene gneiss - Isle of Harris
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Fact sheet
Description: 

This Lewisian rock is from Cleit Thorro, north west of Rodil on South Harris in the Western Isles of Scotland. It was originally a gabbro, intruded in the Archaean period, later metamorphosed in the Laxfordian orogeny when subjected to high temperature and pressure.

In thin section the rock contains large grains of garnet, pyroxene, scapolite, biotite and plagioclase, indicating deep burial and a very high grade of regional metamorphism. The garnet exhibits coronal textures, where rims of minerals reacted with other minerals in the rock as it cooled and decompressed on its journey back to the Earth’s surface following the peak of metamorphism. The rock thus contains evidence of both the prograde path (formed at the peak of metamorphism) and the retrograde path (reactions between minerals as they moved back towards the Earth’s surface).

In Place
In Time
infoImage: 
Location description: 
Cleit Thorro, north west of Rodil, South Harris, Western Isles, Scotland
Accuracy:
Location precision: 
Poor
Timescale:
Timescale: 
Archean
Ma = Millions of years ago
In Focus
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Type:
Type: 
metamorphic
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