Tourmaline greisen - St Austell
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Fact sheet
Description: 

This sample originates from Goonbarrow china clay pit, St Austell, Cornwall, which is one of many greisen areas bordering aplite veins. The greisens were caused by fluids flowing through the veins early in the mineralisation sequence and were associated with hydraulic fracturing of the country rock. The greisens are commonly associated with tin, tungsten and copper mineralisation.

In thin section the rock is rich in quartz and equidimensional tourmaline grains exhibiting characteristic patchy brown/blue colouring and low second order birefringence colours. Fine-grained topaz is also very common and appears to have replaced large areas of the pre-existing minerals. Original feldspar has been entirely replaced mainly by fine-grained sericite.

In Place
In Time
infoImage: 
Location description: 
Goonbarrow china clay pit, St Austell, Cornwall
Accuracy:
Location precision: 
Moderate
Timescale:
Timescale: 
Permian
Ma = Millions of years ago
In Focus
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Type:
Type: 
igneous
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