Siderophyllite Granite - Luxulyan 2 (#201)
 >View Microscope
Fact sheet
Description: 

This sample of granite comes from Luxulyan, St Austell, Cornwall. It is known locally as biotite granite, although the dark mica is the aluminous species siderophyllite. The granite actually contains two mica species - siderophyllite and muscovite. This granite represents part of the main mass of the St Austell granite, and it was this pluton that drove much of the heating and fluid infiltration of local rocks leading to further intrusions and mineralisation. Adjacent mineral deposits and the large clay pits were also the result of the hydrothermal fluid circulation surrounding the SW England pluton during its intrusion in the Permian period.

The thin section contains large plates of biotite showing alteration to chlorite, with lesser amounts of equally sized muscovite. Large plates of quartz show little deformation, orthoclase and plagioclase feldspar are both altered, plagioclase exhibits compositional zoning and orthoclase exhibits coarse perthite textures. 

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

Rock forming mineral:

What\