There are very few earth caches in the area and non which are accessible to the less mobile so I thought I’d add one in this lovely park.
There are few other well maintained caches in the park too.
Ok, so to the earth lesson
At the location given you will find a large, out of place rock. This rock has some interesting formations and the funny lines in it are what you need to study.
The rock you are looking at is a mudstone, this is a type of sedimentary rock. Sedimentary rock is a layered rock, usually fine grained sometimes with larger lumps embedded (though the layers may not be horizontal) and has defined lines in the rock of different colours like reds, yellows or blues. These lines can be as thin as a pencil or hundreds of meters thick. Mudstone rocks are grey/green in colour and have thin defined layers. They feel sharp in one axis and smooth in another. They are sometimes wrongly categorized as slate, but don't 'split' in the way slate would normally do.
The mudstone here has been invaded by a mineral as it formed and your main geological task is to identify the mineral. Below I have described three different minerals; you need to read the descriptions and tell me which mineral has formed here, in the questions below.
Pyrite – iron pyrites
Colour: brassy yellow
Streak: greenish-black
Layers: Medium 20mm to thick 50mm
Texture: Looks like a box of golden dice cubes
Shiny: shiny metallic
Hardness: Moh's scale 6
Looks like gold, also called "fools' gold"
Quartz - crystal
Colour: several possible, often white, clear, or pink
Streak: colourless or light coloured
Layers: From thin 1mm to medium 20mm
Texture: smooth/fractured in the direction of the plane
Shiny: glassy lustre in crystal form
Hardness: Moh's scale 7
Looks like a sheet of fractured and dirty glass
Hematite
Colour: steel grey( when first exposed to air), reddish brown (after exposure to air/water)
Streak: red brown rust colour
Layers: Very thin 0.05mm to thin 5mm
Texture: Smooth, like a fine sandpaper
Shiny: metallic
Hardness: varies on Moh's scale 1-6.5
Other: important ore of iron, used to make steel
in its reddish form, the redness is caused by the rusting (oxidizing) of the iron inside
OK so you should be able to deduce which mineral is present in this piece of rock, so time to answer some questions.
- Describe the aspects of the rock relevant to Q2, be a little more creative than wet and cold please.
- What mineral is present in this piece of mudstone?
- The rock has been placed here for a particular reason, what is that reason?
If you feel willing and able please include a photo in your log of something interesting you saw in the park today, do not include the rock itself. Try to be creative, make me smile.
Please don’t worry if you get it wrong, I just like people to have a go.
Thank you for visiting this cache and I hope that you learned something and though it was worthwhile.