Tourmaline greisen - St Austell
Collection:
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Object

Fact sheet

Tourmaline greisen - St Austell

This sample originates from Goonbarrow china clay pit, St Austell, Cornwall, which is one of many greisen areas bordering aplite veins. The greisens were caused by fluids flowing through the veins early in the mineralisation sequence and were associated with hydraulic fracturing of the country rock. The greisens are commonly associated with tin, tungsten and copper mineralisation.

In thin section the rock is rich in quartz and equidimensional tourmaline grains exhibiting characteristic patchy brown/blue colouring and low second order birefringence colours. Fine-grained topaz is also very common and appears to have replaced large areas of the pre-existing minerals. Original feldspar has been entirely replaced mainly by fine-grained sericite.

Additional images
  • tourmaline greisen - width 4 cm
Map
50.3881, -4.8008
Description:
Goonbarrow china clay pit, St Austell, Cornwall
Precision:
Moderate
About this collection

The United Kingdom Virtual Microscope (UKVM) collection consists of igneous, sedimentary and metamorphic rocks from around the UK.

It is intended as a teaching resource, helping to tell the story of the common rock types and how they form, and reflecting the history of the UK at the margins of the continent of Europe. The collection is a series of teaching sets, for example igneous rocks from the North Atlantic Igneous Province and SW England; high-temperature metamorphic rocks from Scotland and low-temperature metamorphic rocks from Wales; and sedimentary rocks, including English limestones and sandstones.

Sample details

Type
igneous
Category
greisen
Rock-forming mineral
topaz
tourmaline
quartz
sericite
mica
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: