Granite - Lundy
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

Granite - Lundy

The Lundy granite complex is an anomaly as it looks very similar to the many of the granites of Cornwall (and Dartmoor), but yet is very much younger at 58.7±1.6 Ma. It is the southernmost complex of the British Paleogene Volcanic Province whose main focus is in NW Scotland and unrelated to the major granite batholith of SW England.

Petrologically it is also unusual as the granite formed from a volatile-rich melt enriched in elements such as Li, F, Rb, Nb, Ta and W. This has created a pale-coloured rock in which the two micas are pale brown lithian siderophyllite and colourless lithian muscovite. A fine-grained secondary muscovite is also present (see all three mica species in rotation 3). Orthoclase shows typical perthite and simple twinning. Rotation 4 shows one orthoclase crystal enclosing a smaller lamellar twinned plagioclase feldspar crystal. It is adjacent to a feldspar-like mineral with apparently curved twinning. This is thought to be cordierite. Quartz exhibiting wavy extinction is abundant and in places is found associated with topaz. The two minerals have similar optical properties, although topaz has much higher relief. Rotation 1 shows topaz enclosed in mica and rotation 5 shows a tiny inclusion in quartz. Note the well-formed quartz and plagioclase feldspar crystals in the latter field of view. The rare needle-like opaque crystals are tungsteniferous columbite.

Additional images
Map
51.169155, -4.673309
Description:
Lundy Island, off the North coast of Devon
Precision:
Good
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
Rock forming mineral
quartz
orthoclase
plagioclase
feldspar
li-mica
Accessory minerals
topaz
cordierite
monazite
xenotime
uraninite
zircon
w-columbite
Category guide  
Category Guide
Title
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow the user to searranite' as well as more speci?c names such as 'breccia'. However, the adjacent descriptiix 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 togge.g. the UKVM contains 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: