Fluorite Granite - Rostowrack (#45)
 >View Microscope
 >View Object
Fact sheet
Description: 

This lithium-fluorine-enriched granite was collected close to the other fluorite granite in this collection, but has been included here because it shows veining and kaolinite development better than sample #42. Both rocks have been subjected to at least two major hydrothermal events. The first phase of hydrothermal alteration caused breakdown of the feldspars, and the second, driven by fluorine-rich fluids ended with fluorite crystallisation (replacement) along cleavages in lithium mica and in voids within feldspar.

Although the hydrothermal fluids pervasively attacked this rock, some were also channelled through veinlets such as the one crossing the centre of the thin section. Here needles of tourmaline crystallised at the vein margins prior to fluorite precipitation indication a change in conditions from boron to fluorine-dominated fluids. 

Kaolinite is notoriously difficult to prepare in thin section (its a soft white clay) and is often lost during sample preparation, however, in rotation 2 the bluish-orange patch (XPL) it has been preserved. This field of view also shows fluorite alteration along cleavages in a lithium mica and two low birefringent crystals of fluorapatite partially enclosed by the lithium mica.

This rock is close to being a china clay resource! 

In Place
In Time
Location description: 
Wheal Prosper section of Restowrack china clay pit, near St Dennis, 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\
Accessory minerals:

Accessory minerals:

What\