Wizard's Mysterious World #2 - Playing with Stones
While travelling, I often encounter breathtaking spots without a geocache. With this series, I aim to change that. In Wizard’s Mysterious World, you'll discover some of the most enchanting places Mother Nature has to offer.
Cwmorthin - General Information
Important!!! Tools are required to accomplish this earthcache. Bring a copper coin and a knife or a piece of glass.
Cwmorthin Quarry is a former slate quarry with a rich industrial history dating back to 1810. Cwmorthin was primarily an underground quarry with a complex network of tunnels. Although the area is no longer used for industrial purposes, the abandoned buildings and mine shafts are silent witnesses to a turbulent history. Despite its successful mining operations, Cwmorthin has a dark past. Working conditions were appalling. Due to the many fatal accidents, the mine was renamed “The Slaughterhouse”.
This earthcache introduces you to the chemical composition of slate through a series of experiments.
Geological Information
Intramolecular vs intermolecular bonding
A molecule is made up of atoms. These atoms are held together by intramolecular bonds. These are strong bonds that can be compared to glue that holds atoms together.
Rocks are made up of many molecules. These molecules are held together by intermolecular bonds. This is a weaker type of bond. It is therefore easier to break intermolecular bonds than intramolecular forces
Cleavage
Cleavage refers to the splitting of stones. This is the phenomenon whereby stones tend to break along certain planes. It occurs mainly in metamorphic rocks. Metamorphic rocks are formed when rocks are subjected to high pressure. Minerals that naturally have flat or elongated crystals (mica, chlorite, talc) rotate and align themselves perpendicular to the direction of greatest pressure. This creates weak planes that easily separate when, for example, the stone is dropped. In some types of stone (e.g. slate), this phenomenon is very easy to recognise.
The cleavage planes can also be explained at the molecular level. The minerals (molecules) align themselves in certain directions due to the high pressure, which means that the intermolecular forces are not equally strong in all directions. The intermolecular bonds within the plane itself are much stronger than the bonds between the planes. When you drop the stone, the weakest bonds break first. In short, the cleavage planes separate.
Hardness of stones
In geology, hardness refers to a mineral's resistance to scratching. The Mohs scale is a scale from 1 to 10 that indicates the relative hardness of a mineral. A soft rock is given a low number (e.g. talc), while a hard rock is given a high number (e.g. diamond). This allows you to compare minerals based on their hardness. Minerals with a low number can be scratched by minerals with a higher number. For example, quartz can scratch calcite, but is scratched by diamond. To determine the hardness of certain rocks, you can conduct your own research. Try scratching the rock with your fingernail, a copper coin, and a knife or piece of glass. The table below can help you. For example, can you scratch the rock with a knife, but not with a copper coin? Then the rock has a hardness of 3.5-5.5.
Logging Requirements
To log this EarthCache, you must answer the questions below. Send your answers by email or via the message centre. I will try to respond as quickly as possible, but feel free to log immediately. Logs that do not meet the conditions will be deleted without warning.
- At GZ, you are standing on a huge pile of dark rocks. Pick up a rock (big enough!) and drop it on the ground. Be careful! What do you observe? What does the cleavage plane look like? What does it feel like?
- Based on what you have observed, what does this tell you about the stone at molecular level?
- What is the hardness of the rock? Use your fingernail, a copper coin and a knife or a piece of glass to determine this.
- Can you find a different type of rock in the area that can scratch your stone or be scratched by your stone? What does this tell you about its hardness?
- Take a photo of yourself, your GPS or a personal item with the lake in the background to confirm your visit.