M10. Garnet-Mica Schist - Galway
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

M10. Garnet-Mica Schist - Galway

This pelite (garnet staurolite schist) is from within the staurolite zone of the Connemara Dalradian Supergroup. The staurolite crystals commonly grow transverse to the schistosity, and so grew after it had developed. The garnet, in contrast, is augened by the schistosity, and so grew earlier. Crenulations may appear in quartz inclusion trails within the garnet porphyroblasts, showing that two phases of deformation had occurred before the garnet grew. 

The Dalradian rocks of Connemara lie to the south of the Highland Boundary Fault (which crosses Ireland from Fair Head to Clew Bay), so it appears that late faulting shunted the Connemara terrain southwards from its original position (north of the HBF) to its present location.

(Thin section is contaminated with carborundum)

Rotation 1 - Three nice staurolite crystals, with good yellow pleochroism. Biotite and muscovite.

Rotation 2 - Muscovite deformed around garnet.

Rotation 3 - Augened garnet in muscovite and biotite, and ‘late’ staurolite pleochroic, tiny tourmaline.

53.561008, -10.124577
Cleggan, Connemara, Co Galway, Ireland
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: