I hope you will have a craic with this Earthcahce about the granite that once had a crack! 

To log the Earthcache walk around the granite sidewalk by Trinity college and by the National Bank of Ireland. Observe the granite slabs and identify those that contain aplite intrusions, observe them and answer the following questions:

1. What is the evidence of cracks in granite at both of the Earthcache locations?
2. At which of the Earthcache location (Trinity Collge or Bank of Ireland) were you able to find a bigger aplite intrusion?
3. How wide is the biggest aplite intrusion which you have found?
4. How thin is the thinnest aplite intrusion which you have found?
5. Describe the color, texture of one of the wider aplite intrusions with your own words.

Feel free to take a photo at one of the EC locations with an object belonging to you and attach it to the log.

Thanks for visiting this Earthcache!

That granite had once a great crack

During my visit in Ireland I was able to enrich my vocabulary with the Irish slang word: craic. As the Irish say, I really hope that you are having a great craic as you are staying or maybe living in Dublin. I really had myself a great craic here and as I was exploring Dublin I came across this granite that used to have a crack as well. However, this time I mean a crack in a geological terms.

Some of the granite slabs used to build the sidewalk around the Trinity College and the National Bank of Ireland had once a greater geological crack. Some of  the granite had a smaller crack. In this Earthcache you will explore the sidewalk granite in two locations, not far from one another. Hopefully you will learn what kind of crack the granites had and why it is not cracked anymore and what had filled the cracks in the granite. I hope that you will learn something new and will have a craic with this Earthcache.

At first glance, we are dealing with granite slabs. Nothing special. However, As we walk by the Trinity College and National Bank of Ireland, let's take a closer look at some of the sidewalk granite slabs. Once we look closer we will realize that some of the granite slabs really stand out.

I have one more request, as you explore the granite on the sidewalk, be very careful and considerate of other pedestrains and watch out for traffic. This area can be very busy at times.

Granite

Before we move on to further details, let's briefly remind ourselves what granite is. Granite is a type of intrusive igneous rock that is formed deep beneath the Earth's surface and consists mainly of quartz, feldspar, and mica minerals. It is one of the hardest and most durable rocks on Earth, which makes it commonly used in construction and architecture. Granite is quite common and can be found all over the world.

Cracks in granite and magmatic intrusions

Granite that is located deep underground can be subject to various processes that can affect its final appearance. One of these processes is the formation of magmatic intrusions. Sometimes, the solid, hard granite located underground cracks under the influence of, for example, tectonic plate movement. If there is high presserized liquid magma around the cracked granite, it will penetrate the cracks in the granite. If the temperature difference between the liquid magma entering the cracks and the surrounding granite is large, a rapid process of crystallization occurs. In this way, the magma entering the fractures quickly solidifies and forms a magmatic rock structure with fairly small crystals, invisible to the naked eye.

Aplite

Aplite is a type of magmatic rock that is similar to granite in terms of mineral composition but is characterized by much finer crystal structure. It mainly consists of quartz and feldspar. It might containe very small traces of other minerals. The grains in aplite are usually microscopic and very uniform.
Aplite forms through the crystallization of magma within the Earth's crust. Aplite can be found particularly in granite intrusions, where it has formed thin, adhesive veins that cut through the main mass of granite. Aplite rock can also occur as a solid rock body near granite.
Due to its structure, appearance, properties and most importantly, durability, aplite is sometimes used as decorative stone in construction.

Source: own photos and own work

Sources:

S.K. Haldar, in Introduction to Mineralogy and Petrology (Second Edition), 2020 
https://geologische-streifzuege.info/aplite/