To log this EarthCache you must answer the following questions:
- Do you think this is Leinster or Galway granite?
- What year is carved on the rock?
- In geology, what are the scratches caused by glacial erratics called?
- It’s an option, but please include in your log a photo of you (or an identifying piece of geocaching kit) at the location.
This EarthCache is aimed at younger Geocachers or those with limited knowledge of Geology.
You are looking at a monumental stone made from granite. Have a look at the back of the stone and you will see shiny bits in granite which are are caused by the mineral mica which is highly reflective and forms in thin, flat flakes. These flakes give granite its characteristic shimmer and sparkle, especially when light hits them.
In Ireland granite is found in Leinster and in Connaught.
Leinster granite is white due to its composition of light-coloured minerals like quartz and feldspar, which are dominant in the rock. The dark minerals present are relatively small in volume, and the overall appearance is a light-coloured rock
Galway granite is pink due to its high content of potassium feldspar, a mineral that commonly exhibits a pink hue. The pink colour can vary in intensity, with some granites appearing pale pink while others are a more vibrant pink or even reddish.
When you have considered the stone type I invite you to consider the rock as a model of what happens in nature.
In geology, an erratic refers to a rock or boulder that has been transported from its original location and deposited elsewhere, often far from its source. These rocks are notably different in composition and origin from the surrounding bedrock and are frequently found in areas that were once covered by glaciers.
In Ireland, movement of glaciers and ice sheets created many erratics. Geologists study their composition and can determine where the rock came from (the source). Once the source is known, the direction of ice flow can be determined. The end of these erratic flow paths are called erratic limits. The Geological Survey of Ireland produces maps to show these paths and limits.
As glaciers move, the erratics they can carry act like sandpaper on the underlying bedrock, creating scratches and grooves known as glacial striations
The rock here at GZ technically meets the above definition as it is Granite and the bedrock in this area is limestone. I’m calling it a ‘modern erratic’ as you can see how external forces have moved it quite a relative distance from its original location. You can also see the scrapes left in the underlying surface as it moved. Its not a true erratic as large lorries rather than glaciers were the forces which moved it. However, it provides a valuable and clear model of all the natural effects!
Congratultions to silver soldier and Eyeash on a joint First To Find.