Granite Porphyry (Elvan) - Littlejohn's (#17)
 >View Microscope
 >View Object
Fact sheet
Description: 

This highly altered granite porphyry dyke comes from Littlejohn's china clay pit, St Austell, Cornwall. China clay in this area was created while the underlying granite was still cooling, when it was fluxed by fluids rich in water, boron and fluorine, attaching the sodium-rich feldspar. Clay is mined in this area by high pressure water hoses and filtering to remove the remaining micas and quartz. Littlejohn's clay pit has been active since the 1800s and continues to supply fine clays suitable for use in paper making.

In thin section the rock contains fine-grained altered plagioclase and orthoclase feldspars, and unaltered quartz phenocrysts. White mica is also common in the thin section.

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

Rock forming mineral:

What\