Tourmaline Aplite - Melbur (#24)
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Fact sheet
Description: 

This sample provides a good illustration of trapped volatiles in a granitic magma. At the very end of the magmatic cycle boron-rich volatiles become concentrated and here they have been preserved in the form of tourmaline "balls" - each representing a bubble of volatiles. See how the volatiles have leached the colour from the surrounding aplite - this represents a solid state migration of elements into and out of the "balls". The rock is an aplite that intruded earlier granite (from the first phase of igneous activity in this region).

In thin section note fine grain size of the matrix, the considerable alteration of feldspar and the pools of tourmaline mantled by quartz.

In Place
In Time
Location description: 
Melbur china clay pit, St Austell, Cornwall
Accuracy:
Location precision: 
Moderate
Timescale:
Timescale: 
Permian
Ma = Millions of years ago
In Focus
Collection:
What\
Type:
Type: 
igneous
What\
Rock-forming minerals:

Rock forming mineral:

What\