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Elements in the Earth's crust

by sophiecentaur
Tags: crust, earth, elements
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sophiecentaur
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Jun9-14, 12:05 PM
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I have just had a trip up Mt. Etna (Sicily). A brilliant trip but it raised a question. There are large patches of colour in the fresh lava, due to Iron, Copper, Sulphur etc.
What mechanisms cause the elements to become separated in the process from Super Nova (all mixed up?) to individual regions under ground? There must be someone on PF who knows about this stuff.
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jedishrfu
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Jun9-14, 01:01 PM
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Could it be explained as an artifact of mixing?

The convective rolls video where beads of 2 sizes are placed in a slowly rotating rectangular prism box.

http://www.wired.com/2009/10/bead-cloud-mystery/

and a writeup about mixing phenomenon:

http://www.phschool.com/science/scie...ing_mixer.html
sophiecentaur
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Jun9-14, 03:26 PM
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Two interesting links there. The failure of things to mix is with us always (someone always gets most of the raisins in the Fruit n Fibre packet. That is a very arm waving but convincing reason not to be surprised by my observation.

I was not so happy with the "fifth state of matter" message, though. There are very few pure solids, liquids, gases or plasmas around and that causes constant confusion for students who want to classify everything they meet with. Another classification just adds to their problems.
It would be interesting to know how common the separated condition is, in comparison with the well mixed state in the Mantle.

jim hardy
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Jun9-14, 06:17 PM
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Elements in the Earth's crust

Recently heard a mining engineer say it's the combined processes of outgassing and cooling in earth's crust wherein
the metals come out as a gas mixed with really hot steam and plate out on the vent holes in rock as the mixture cools to the metals' melting point.

Though he was speaking of granite in Colorado , and it was an 'off the cuff' remark, it sorta explained veins, like soot depositing inside a chimney. Gold vaporizes around 2600 C while water starts dissociating ~2200 C so it probably involves considerable pressure too.

Just offered up as food for thought not solid science . It sounded plausible to this old electrical type.

old jim
sophiecentaur
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Jun10-14, 02:54 AM
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So we're talking in terms of several different processes. That's fine. Just like the different departments in a chemical factory.
It seems to be almost as difficult to produce a really good mix as to produce a really pure product. Hence, my patches of sulphur on the volcano. (Note the correct spelling of "sulphur', folks. Haha)
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RonL
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Jun10-14, 11:06 AM
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jim hardy's post brought a thought of mine to recollection, being a gold prospector at the hobby level, I had tried to understand how gold is deposited in such tiny cracks, fissures and pores of certain formations.
The movement of large masses of rock formation during an earthquake in vertical and horizontal directions to each other, should produce strong vacuums in areas of separation where even modest heat would generate a vapor deposition process of any elements in the area. Just a few seconds of extreme energy displacement and a process that I had always thought took very high temperatures, can happen at far lower heat than the melting points of most elements.

Size can be of any order that one wants to consider, IIRC the island of Japan was recently shifted on both vertical and horizontal planes :)

Ron
sophiecentaur
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Jun10-14, 12:51 PM
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Fractional state change to separate the different substances - kind of thing. Like getting ice out of vodka in the freezer. Then the heavy stuff would sink and gather.
I wish we had a vulcanologist on tap.
256bits
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Jun12-14, 07:31 AM
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Quote Quote by sophiecentaur View Post
I have just had a trip up Mt. Etna (Sicily). A brilliant trip but it raised a question. There are large patches of colour in the fresh lava, due to Iron, Copper, Sulphur etc.
What mechanisms cause the elements to become separated in the process from Super Nova (all mixed up?) to individual regions under ground? There must be someone on PF who knows about this stuff.
Question: How do you come to say it is due to Iron, Copper, Sulpur, ... ? There should be ores of these elements, the minerals and ores are often difficult to discern which is which.

Depending upon the temperature of the melt, certain crystals grow and precipitate in the magma below the surface, and accumulate. Upon eruption some of these crystals can be brought out to the surface with the flow.

Most lava contains water and water can contain ions. Depending upon what the water does as the lava cools, such as evaporating or combining with some minerals, there should be different compositions of substances as the concentrations evolve. Not sure how far I could go on this at the moment, refresh needed, but this should be a factor.

What type of flow were you looking at? Lava flows come in all sorts - fast, slow, thick, thin, so the viscosity could tell you some more of its composition and constituent liquids and minerals.
sophiecentaur
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Jun12-14, 12:34 PM
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The guide ( no Chemist!) mentioned the colours and referred to element "colours". Not well put but it made me think about separation processes. If it were not for them there would have been no Bronze Age or later recognisable technologies.
What we saw was patches of colour on distant crater slopes so I don't know about the thicknesses of layers.
I assumed the bright yellow was elemental sulphur. Is that likely?
The stuff we saw was in a crater formed since 2000. It was a massive, explosive eruption, apparently; it formed a small mountain when it fell back down.
256bits
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Jun12-14, 07:35 PM
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Outgassing of vents around active reagions.
The gases would sublime.
So, in the case of sulphur, that is a common way of elemental sulphur to form.
Besides of course all the other sulfides, stinky H2s for one, that get released into the atmosphere and form as ores and minerals containing sulphur around the volcano.

Brimstone mining was one way to get sulphur in the early days as well as scare the crap out of people with Fire and Brimstone tales of punnishment from the gods.

Here is an article on mining sulphur from an active volcano.
http://www.bbc.com/news/world-asia-pacific-12301421

From the article,
Pipes are driven into the fissures in the rock to extract sulphur from the bowels of the mountain. It is blood red when molten, and turns yellow as it cools and solidifies.
Now how do they get elemental copper and iron?


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