M01. Amphibolite - Lough Nagilly, Donegal
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

M01. Amphibolite - Lough Nagilly, Donegal

An amphibolite raft in the Thor Granite (Caledonian). The sample was collected from a huge xenolith, or raft, enclosed within the Thor pluton, which is one of the component plutons of the Donegal Granite batholith. The random orientation of the hornblende and plagioclase grains is consistent with thermal metamorphism, with no directed stress, and the brown colour of the hornblende suggests that the conditions were at the high-temperature end of the spectrum of amphibolite-facies conditions. The protolith was a basic intrusion from about 600 Ma which was one of many such intrusions invading the Dalradian Supergroup sedimentary rocks before they were first metamorphosed during the Grampian Orogeny (470 Ma). This amphibolite was totally recrystallized by the heat from the surrounding granite about 400 Ma. Rotation 1 - Best cross section of hornblende with two sharp cleavage traces and symmetric extinction. Rotation 2 - Twinned hornblende 15° extinction to twin plane. Also twinned plagioclase.

54.962625, -8.262453
About this collection

A group of iCRAG members (UCC, TCD, NUIG and UCD) in partnership with The Open University have created a new collection of Irish rocks and associated learning materials for the Virtual Microscope of Earth Sciences.

The project which is entitled 'The Geoscience e-Laboratory (GeoLab): Developing Digital Teaching and Learning Resources for the Virtual Microscope' seeks to develop open access teaching resources in the form of interactive exercises and assessment rubrics for the Virtual Microscope. Find out more about the project at the GeoLab website.

The Collection was created using funding from the Faculty of Engineering, Mathematics and Science at Trinity College, Dublin, and the National Forum Teaching and Learning Enhancement Fund. One sample (Merensky Reef) showcasing x-ray element maps in addition to the usual PPL/XPL/REF images was funded by Prof. Balz Kamber's MetalIntelligence EU training network grant.

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: