DO YOU KNOW YOUR ROCKS #2 EarthCache
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DO YOU KNOW YOUR ROCKS #2
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Do you know your rocks #2 Pumice and Scoria
The object of this series of earthcaches is to teach and inspire people to be able to recognize and apreciate the rocks and rock formations that are around them and understand how they came to be.
Firstly to recognize different types of rock you need to know what they look like, what they look like is mostly of what they made of, but more importantly is what mothernature has done with what she had to work with.
Like an artist, nature uses different media to make different rocks, whether its wind, water, heat,pressure or anything that the earth has in its arsenal.
Scoria and Pumice start with Magma deep inside the earth, some magma have different visconsity (how thick a liquid is) than others due to theyr mineral and compound makeup. mafic magma is less viscous than felsic magma.some magma also have dissolved gas in it.
And this will inevitably determine whether pumice or scoria gets formed.
As the magma rises to the surface it starts creating gas pockets, but because it is still under tremendous amounts of pressure it is in all sence still a liquid- like the liquid that's inside a lighter or a gas bottle. When magma rises to the surface the "liquid" gas starts expanding. Depending on the visconsity of the magma these bubbles of gas react in two ways, the felsic magma is more viscous (thicker) than mafic magma (thinner) so the bubbles(vesicules) can't join up.
Where as in mafic magma the bubbles can join up and form larger bubbles.
Let's compare a volcano to a bottle of softdrink, if you shake it up and open the bottle cap quickly the gas will expand and rocket into the air with foam all over the ceiling.
If we open a bottle of say thick tomato sauce that's hot and and you open the lid quickly it kinda blobs out.
That is basically the two extremes how a volcano can erupt depending on the visconsity and the pressure under wich the magma is.
When it is the more viscous (thicker) magma type of eruption (like the tomato sauce) it is called a strombolian eruption, these eruptions are slow in the sence that its not a violant BANG explosion, but they do explode, the lava get flung into the air two metres or two hundred metres in the air, kind of like a pot of porridge that is filled to the brim.
When the magma is less viscous(thinner) the pressure tends to build up much more, and when the super heated magma breaches it is much more of a BANG!!!.like When a pressure cooker is on the stove and all of a sudden the cooker releases the steam.
When the molten magma erupts in both situations, the lava cools down suddenly and traps the bubbles of gas(vesicles) within the "rock"
These cooled down magma forms rock formations that have vesicles (air pockets).
The size of these pockets are determined by the visconsity of the the magma in wich they they formed.and this will determine whether it is Scoria or Pumice.
Some facts of Scoria and Pumice
SCORIA
Igneous Rock Type: Extrusive
Realated to: Basalt, Obsidian, Pumice
Chemistry: Basic to intermediate
Colour: Blackish brown to red
Texture: Glassy
Origins: Volcanic Lava Flows and Ejecta
Uses: Decorative stones, Grilling stones
PUMICE
Igneous Rock Type: Extrusive
Related to: Rhyolite, Obsidian, Scoria
Chemistry: Intermediate to Basic
Colour: White to light green
Texture: Glassy
Origins: Genaraly from Volcanic Arcs
Uses: Abrasive or Scouring stones, Filter media
The on site questions are as follow
1. The rock formations , is it Scoria or Pumice?.
2. In your own words describe the colour and texture of the rock formation.
3. Describe the two man made objects that are within a 20m radius of GZ
4.What type of protected flower grows at GZ
5. Take a pic of the view( this is optional) but it is a nice view.
Forward your answers to
Our Kingosric handle name within 3 days to not get your log deleted.
The information used in this writeup was acquired through:
Wikipedia
Geology.com
Mineral gallery
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