๐จYou are best walking to the EarthCache location.ย The road from Helwith Bridge, is often busy with quarry waggons. ๐จ
In geology people tend to look for the larger features, as they are easier to see, though sometimes smaller things can catch the eye, and then lead to interest and understanding.ย In some locations, looking at the rocks which make up the anatomy of a wall can give interest, and also learning about geology.ย The below photograph shows a wall in nearby Little Stainforth, which demonstrates the geology of the local area.ย
- (Photograph: Hillgorillas' wall).
We are here to look at an aspect of geology on a macro level. You would benefit from having a camera๐ท or mobile phone๐คณ that can take an image on a macro level, or a magnifying glass๐. The below photograph shows where to look. DO NOT MOVE ANY STONES.ย
The geology of the wall.
The wall is made up of greywacke, which was deposited during the Silurian period, which was 445 to 420 millions of years ago.ย Geologically, itsย story starts in an ancient ocean known as the Iapteus Ocean. Sediment in the form of sand and silt was laid down on the ocean floor, then turbulent movement of the sea bed occured. Over time sediment built up , and eventually rock was formed. However this is not the end of the story. The Iapteus Ocean dissapeared eventually, and the sedimentary layers were uplifted and folded due to massive tectonic forces. The rock was also subjected to metamorphism, which is where pressure and heat alter the structure of the rock.
What are we here to look for?
Well, it's something rather special called Fools Gold, but before you demolish the wall, and head for a jewellers, it is not actually gold. It is called iron pyrite.ย
So what is Iron Pyrite?
It is an Iron Sulphide, and is found in all types of rock โ (igneous, metamorphic and sedimentary) as well as in hydrothermal vents. Its formation can be in a variety of ways:
Igneous Rocks. In this situation it is formed from the minerals in magma, which seperated out, depending on the temperature as it cooled, with crystals being formed.ย
Metamorphic Rocks. These rocks are formed by heat and pressure, and in this situations, the pyrite could have been formed as the process of metamorphism takes place, or as a replacement mineral in the rock.
Sedimentary Rocks.ย With this type of rock, pyrite is usually found as a replacement mineral,ย whenย iron and sulphur present in the sediments combine to replace the original chemical composition of organic matter.ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย ย
Pyrite crystals can form as framboids or cubesย depending upon the temperatures and pressures.
Cubes commonly form as a result of fluid rich diagenesis or low-grade metamorphism. Diagenesis means the change of a rock, after initial depositionย into a different form. It can take place due to a chemical, biological and physical change due to reasons such asย temperature, pressures, and saturation with groundwater. They are formed due to authigenesis, which occures when a mineral deposit is produced where it is found. Once the cubes have formed, the pyrite becomes refractory, and can keep its features even when the rock has becomes deformed. Refractory means it isย resistant to decomposition by heat, pressure, or chemical attack.
Framboids have spherical features, like the parts of a raspberry.ย
This being an EarthCache, in order to log it, I ask that you answer the below 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 examine the rock, and explain how the iron pyrite appears, in terms of colour and are there cubes or framboids.ย ย
2. If you were here explaining it to someone with no knowledge of geology, how in your own words would you describe the Fools Gold geologically?
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