Porphyritic felsite - Isle of Rum
Collection:
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Fact sheet

Porphyritic felsite - Isle of Rum

This sample of Porphyritic Rhyodacite (known as ‘Porphyritic Felsite’ in early accounts) comes from the Rum Central Igneous Complex of the Paleocene North Atlantic Igneous Province. It formed a caldera-filling ignimbritic flow and was found on the Col between Sgurr nan Gillean and Ainshval, Southern Mountains Zone. The rock was part of Phase 1 of the Rum Central Complex, one of the silicic magmas accompanying ring-faulting and caldera formation.

The thin section contains phenocrysts of zoned plagioclase and quartz (commonly corroded) in a fine-grained, equigranular quartz-feldspathic matrix with irregular crystals of green hornblende and relic pigeonite and augite, and magnetite. 

Additional images
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
felsite
Rock-forming mineral
quartz
alkali feldspar
pyroxene
hornblende
plagioclase
feldspar
Accessory minerals
zircon
magnetite
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: