Explosion Breccia - Wheal Remfry (#12)
Collection:
Click the microscope button to view a thin section for this sample.
Microscope
Click the microscope button to view a thin section for this sample.
Microscope
Click the object button to view an object rotation for this sample.
Object

Fact sheet

Explosion Breccia - Wheal Remfry (#12)

The Wheal Remfry china clay pit lies at the western end of the St Austell granite complex.The clay pit yields white clay suitable for use in the ceramic industry rather than the more refined clays used in paper making. This explosion breccia provides evidence of the enormous pressures that can build up in trapped hydrothermal fluids. This rock mainly consists of fragments of sediment brought up from depth by the high pressure fluids.

In thin section the rock is dominated by fine-grained bands of tourmaline and quartz that have replaced the original detrital minerals of the sediment. At this scale, the rock consists of a series of fragments welded together and metasomatised by the fluids.

Additional images
  • width 6 cm
  • width 15 cm
  • width 15 cm
  • width 15 cm
  • width 3,5 cm
Map
50.382316, -4.921317
Description:
Wheal Remfry china clay pit, St Austell, Cornwall
Precision:
Good
About this collection

A case study of the St Austell granite complex in Cornwall, England, illustrating the range of rocks associated with a granite intrusion. The earliest part of the complex is a siderophyllite (biotite) granite containing muscovite and tourmaline typical of a SW England granite, with many primary magmatic features.

This early intrusion was followed by the intrusion of an evolved volatile-rich magma which was the driving force behind a series of intense hydrothermal processes as volatiles escaped from this magma and helped to establish an extensive alteration halo (aureole). Boron, fluorine and lithium (as well as water) played major roles in the formation of the second intrusion and in the associated hydrothermal processes. Igneous activity lasted around 18 million years from 282 Ma (siderophyllite granite) to 265 Ma (fluorite granite).

 

Sample details

Collection: St Austell Granite
Type
igneous
Rock-forming mineral
tourmaline
quartz
Category guide  
Category Guide
Title
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow users to search for broad terms like ‘granite’ as well as more specific names such as ‘breccia’. However, the adjacent descriptions of the specimens captures a wider range of general words and phrases and is a more powerful search tool.
Description
Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Timescale
Selecting one or more period, for example 'Jurassic'.
Theme
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
Category
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
Owner
The owner of the sample that appears in the collection. For example, NASA owns all the samples that appear in the Moon Rocks collection
We would like to thank the following for the use of this sample: