War Memorial #847 ~ Ballachulish EarthCache

Ballachulish war memorial, stands above the road between Glen Coe and Ballachulish, and overlooks Loch Leven. Take your time to look at this memorial, and look in to the eyes of the kilted soldier, as he will look into yours. Pay your respects to these brave men. 

This is an EarthCache, and we are here to look at the stone that makes up the memorial. You will need to look all arond the memorial.  The memorial is made from Granite. 

Granite is a common type of igneous rock. Igneous rock  is one of the three main rock types , the others being sedimentary   and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as  extrusive (volcanic)  rocks. Granite can be white, pink, or gray in colour, depending on their mineralogy.  Granitic  rocks mainly consist of feldspar, quartz, mica and amphibole minerals,  which form an interlocking matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter colour minerals.

There are many EarthCaches which look at granite in detail, we are here to look at what are known as  phenocrysts, but to look beyond their basics. 

A phenocryst is a crystal in igneous rock, which is larger than the crystals of the rock that it forms part of. 

Phenocrysts can have different forms:

Euhedral - these crystals are well defined, sharp and easily recognisable edges. 

Anhedral – these crystals do not have well defined edges.

We are here to look at the alignment of phenocrysts. 

Variations in the size, volume and orientation of phenocrysts can tell us more than just a collection of large crystals in an igneous rock.

The size of phenocrysts change depending on where they were formed in the flow of the igneous rock as it cooled. Concentrations of phenocrysts  are found to be nearly zero at the margins of the flow , and their size increases inwards towards the centre of the flow.  The increase in size and abundance of phenocrysts toward the center of the dike is interpreted as resulting from flow differentiation.

Flow Differentation

This is the change of the composition of magma as it cools, as this happens different parts of the magma cool at different rates, and this this gives rise to different flows within the magma which have different temperatures, in the this different flow, crystallisation of the rock takes place at different rates. Also contamination the magma by the wall rocks melting into it from the walls of the magma chamber can affect the make up of the magma and its flow rate. 

The primary cause of change in the composition of a magma is cooling, which is an inevitable consequence of the magma being created and migrating from the site of partial melting into an area of lower stress - generally a cooler volume of the crust.

The alignment of phenocrysts can help to show the direction of the magma flow, which can be shown by phenocryst  alignment parallel to the direction of supposed flow. 

This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.

1. Please take your time to examine the war memorial. There is an area on the memorial which shows phenocyrst allignment:

(a) Which aspect of the memorial is this on (ie the north, south, west or east face of the memorial)?

(b) Which direction do these phenocrysts point (i,e, upwards, downwards, horizontally, at an angle)?

(c) What colour are these phenocryts? Please mesure the length of the longest phenocryst. 

(d) How many phenocrysts are in this group of alligment phenocrysts? 

(e) Are the phenocrysts euhedral and anhedral?

2. Please have your photograph taken with yourself and the war memorial.