Luxullianite - Shabby Rocks Field (#03)
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Fact sheet
Description: 

Luxullianite is a rare type of tourmaline-rich granite named after the village of Luxulyan in Cornwall. Luxullianite is formed from boron-rich pegmatitic fluids caused by fractional crystallisation of the earlier biotite-rich St Austell granite complex, which formed around 280 million years ago by partial melting of the lower continental crust during the Variscan orogeny. In hand specimen the rock appears to consist of two main parts – striking salmon pink tabular feldspar shapes, and black tourmaline that appears to be infilling voids. 

This sample of Luxullianite illustrates two phases of tourmaline crystallisation: an early blocky magmatic phase exhibiting characteristic tourmaline colours, and tourmaline radial sets of needles forming ‘suns’ that grew late in the formation of this rock. Crystallisation in cavities has allowed the rock to develop fine rosettes of acicular crystals with characteristic brown-blue-green pleochroism and vivid birefringence. Zircon and the tin ore mineral cassiterite complete the mineral assemblage.

In Place
In Time
Location description: 
Shabby Rocks Field, near Luxulyan, St Austell, Cornwall
Accuracy:
Timescale:
Timescale: 
Permian
Ma = Millions of years ago
In Focus
Collection:
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Type:
Type: 
igneous
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