Serpentinised peridotite - Lizard
Click the microscope button to view a thin section for this sample.
Click the microscope button to view a thin section for this sample.

Fact sheet

Serpentinised peridotite - Lizard

This sample of altered peridotite forms part of a suite of rocks (the Lizard Complex in Cornwall) that represents a cross-section of Devonian-age oceanic crust, from surface volcanic rocks deep into the peridotite of the underlying mantle. The Lizard Complex, preserved during the continent–continent collision known as the Variscan orogeny, is the best example of an ophiolite complex in the UK. Although this peridotite originally formed as an igneous rock composed mostly of olivine, it has been completely altered to serpentine by interaction with sea water.

In thin section the rock appears pale green, a colour caused by the serpentine minerals that are formed by the breakdown of olivine. Other clay minerals and metal oxides (opaque in thin section) are also formed by breakdown reactions and are evident in the thin section. The alteration minerals are found in cracks and veins where fluids penetrated the rock on scales from one millimetre down to a few microns. Fragments of olivine remain, and can be observed as small highly birefringence grains separated by networks of veins filled with alteration products. Partially altered olivine fragments are most prominent in the upper right-hand quadrant of the thin section. The remaining large grains in the thin section are highly cracked and veined pyroxene, and dark-brown-coloured spinel that is also cracked but exhibits less alteration.

Additional images
  • peridotite - width 7 cm
  • peridotite (wet) - width 3 cm
50.0194, -5.1479
Lizard Peninsula in Cornwall
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

Rock-forming mineral
Accessory minerals
iron oxide
Category guide  
Category Guide
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.
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.
Selecting one or more period, for example 'Jurassic'.
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.
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).
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: