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Author Topic: Is volcanic rock more radioactive ?  (Read 17741 times)

ROBERT

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Is volcanic rock more radioactive ?
« on: 22/05/2006 11:51:19 »
Is volcanic rock more radioactive than sedimentary rock ?, if so why ?.
« Last Edit: 22/05/2006 11:51:40 by ROBERT »


 

Offline Bass

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Re: Is volcanic rock more radioactive ?
« Reply #1 on: 23/05/2006 03:16:21 »
Depends on the rock.
(there's a definitive answer for you;))

Some sedimentary rocks have high concentrations of radioactive elements- including carbonaceous shales, phosphates, coal, muds and sandstones.  There is still considerable debate on whether or not the uraninite in the Witwatatesrand is sedimentary.

Silicic volcanic rocks (and their plutonic equivilents) commonly are enriched in radioactive isotopes, especially potassium.

Subduction causes orogeny.
« Last Edit: 23/05/2006 23:11:26 by Bass »
 

Offline JimBob

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Re: Is volcanic rock more radioactive ?
« Reply #2 on: 24/05/2006 00:09:44 »
The uranium "mines" in here in Texas are in sedimentary rocks - sandstone. They are "mines" ander the legal definition. These are actually boreholes that inject water into the sand and withdraw it from the ground on the other side of the ore deposit.


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ROBERT

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Re: Is volcanic rock more radioactive ?
« Reply #3 on: 24/05/2006 12:49:37 »
Thankyou Bass and JimBob.
Could you tell me what are the processes by which radioactive elements would become concentrated in particular rocks.
 

Offline Bass

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Re: Is volcanic rock more radioactive ?
« Reply #4 on: 24/05/2006 16:56:23 »
The three most abundant naturally occurring radioactive elements are uranium, thorium and potassium (along with their daughter products).  
The radioactive isotope of potassium is K40.  While K40 only makes up about .01% all potassium, the abundance of potassium in certain rocks means that there will also be a relative abundance of K40.  Potassium has an affinity for more silicic igneous rocks (granites and rhyolites), is elevated in most hydrothermal systems and is common in soils and certain sedimentary rocks.  Potassium is a common constituent of feldspars and clays.
Uranium and thorium, beause of their large atomic size, do not readily combine with other elements to form common rock forming minerals.  As such, they tend to accumulate in the more volatile remnants of (especially silicic) igneous rocks- meaning they tend to accumulate in last parts of the magama to crystalize (pegmatites) and in the veins associated with silicic magmas.  So you won't find much uranium and thorium in Hawaii or Iceland- it is much more likely in continental igneous rocks.  Granitic rocks and rhyolitic volcanic rocks will contain higher than normal crustal abundances.  Uranium minerals include uraninite and pitchblende (uranium oxides) as well as several species of uranium vandates and phosphates.
Uranium is also very eH sensitive- it goes into solution in oxidizing conditions and precipitates in reducing conditions.  Many of the world's economic uranium deposits form "roll fronts" in sandstones.  The sandstones are permeable- allowing water to flow through them.  As the water flows down-dip, conditions change from oxidizing to reducing and uranium is precipitated at redox boundary.  Any organic matter in the sandstones can cause local reducing conditions- uranium minerals commonly replace fossil logs, stumps etc.
Uranium is commonly elevated in coal, shales, phosphate deposits- as these sedimentary rocks tend to be found in reducing conditions.

This long post just barely scratches the surface of uranium depostion- I labored many years in uranium exploration- but hope it helps.


Subduction causes orogeny.
 

ROBERT

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Re: Is volcanic rock more radioactive ?
« Reply #5 on: 24/05/2006 17:16:34 »
Thank you for replying to my question Bass.

quote:
Originally posted by Bass

 I labored many years in uranium exploration.


Hopefully you don't glow in the dark as a result :).


I have read that there are boozy bacteria which can concentrate Uranium:-

" After adjusting pH, the researchers provided weekly additions of ethanol to the recirculating water for more than a year. The ethanol stimulated growth of subterranean microbial populations that converted the uranium into an immobile form. After treatment, high levels of uranium remained on the soil, but the groundwater contained almost no uranium. Analysis of the soil-bound uranium confirmed that it was largely converted into the immobile form. "
http://www.physorg.com/news67270244.html



« Last Edit: 24/05/2006 17:33:38 by ROBERT »
 

Offline Bass

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Re: Is volcanic rock more radioactive ?
« Reply #6 on: 24/05/2006 17:39:38 »
Did I fail to mention biogenic precipitation?[B)]

All that radioactivity must have affected my brain?  Or maybe its just age?

I have studied sevaral uraniferous shales with rounded blebs of pyrite (precipitated by bacteria?)- almost all the uranium in these shales is associated with the pyrite- I assume mainly due to biogenic precipitation.

Subduction causes orogeny.
« Last Edit: 24/05/2006 17:50:18 by Bass »
 

Offline kola

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Re: Is volcanic rock more radioactive ?
« Reply #7 on: 19/06/2006 20:01:24 »
quote:
Originally posted by Bass

Depends on the rock.
(there's a definitive answer for you;))

Some sedimentary rocks have high concentrations of radioactive elements- including carbonaceous shales, phosphates, coal, muds and sandstones.  There is still considerable debate on whether or not the uraninite in the Witwatatesrand is sedimentary.

Silicic volcanic rocks (and their plutonic equivilents) commonly are enriched in radioactive isotopes, especially potassium.

Subduction causes orogeny.

 

Offline kola

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Re: Is volcanic rock more radioactive ?
« Reply #8 on: 19/06/2006 20:06:53 »
Hi, does anyone know if the amount of radiation exposure from volcanic rocks poses a health hazard (especially over time).  I have some rock samples as "souvenirs" from Mt. Pinatubo in the Philippines, as well as lahars.  The locals there also make sculptures out of the volcanic rock and ash, and i have one of these sculptures.  Thanks





quote:
Originally posted by Bass

The three most abundant naturally occurring radioactive elements are uranium, thorium and potassium (along with their daughter products).  
The radioactive isotope of potassium is K40.  While K40 only makes up about .01% all potassium, the abundance of potassium in certain rocks means that there will also be a relative abundance of K40.  Potassium has an affinity for more silicic igneous rocks (granites and rhyolites), is elevated in most hydrothermal systems and is common in soils and certain sedimentary rocks.  Potassium is a common constituent of feldspars and clays.
Uranium and thorium, beause of their large atomic size, do not readily combine with other elements to form common rock forming minerals.  As such, they tend to accumulate in the more volatile remnants of (especially silicic) igneous rocks- meaning they tend to accumulate in last parts of the magama to crystalize (pegmatites) and in the veins associated with silicic magmas.  So you won't find much uranium and thorium in Hawaii or Iceland- it is much more likely in continental igneous rocks.  Granitic rocks and rhyolitic volcanic rocks will contain higher than normal crustal abundances.  Uranium minerals include uraninite and pitchblende (uranium oxides) as well as several species of uranium vandates and phosphates.
Uranium is also very eH sensitive- it goes into solution in oxidizing conditions and precipitates in reducing conditions.  Many of the world's economic uranium deposits form "roll fronts" in sandstones.  The sandstones are permeable- allowing water to flow through them.  As the water flows down-dip, conditions change from oxidizing to reducing and uranium is precipitated at redox boundary.  Any organic matter in the sandstones can cause local reducing conditions- uranium minerals commonly replace fossil logs, stumps etc.
Uranium is commonly elevated in coal, shales, phosphate deposits- as these sedimentary rocks tend to be found in reducing conditions.

This long post just barely scratches the surface of uranium depostion- I labored many years in uranium exploration- but hope it helps.


Subduction causes orogeny.

 

Offline kola

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Re: Is volcanic rock more radioactive ?
« Reply #9 on: 19/06/2006 20:14:23 »
Hi everyone,

I am new to the forum.  I read the posts about the presence of radioactive materials in volcanic rocks, and am wondering if the level of radioactivity that is emitted from volcanic rocks poses a health hazard (especially over time).  I am not a scientist, but cannot find good information on the topic anywhere else on the internet.  Can anyone here address my question or refer me to someone who can, preferably someone who has familiarity with Mt. Pinatubo?

I have a number of "souvenirs" from that volcano, including rocks, lahar, and a sculpture made of volcanic rock (maybe packed ash).  I understand that eruptions are powered by radioactive decay, so is the amount of radiation in volcanic rocks enough to, over time, pose unhealthful risks, sort of like radon gas in basements or excessive sun exposure?  
Thanks for anyone's help.
 

Offline Bass

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Re: Is volcanic rock more radioactive ?
« Reply #10 on: 19/06/2006 20:53:24 »
Given the small size of the samples (and sculptures), the minute concentrations of radioactive minerals, and the long time period of radioactive decay, I'd guess you are more likely to be simultaneously hit by lightning and eaten by a bear than to be harmed by radioactivity from your collection.  Of course, the lightning probably won't do the bear much good either.;)

Subduction causes orogeny.
« Last Edit: 19/06/2006 20:54:16 by Bass »
 

Offline daveshorts

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Re: Is volcanic rock more radioactive ?
« Reply #11 on: 20/06/2006 10:15:58 »
Living on a couple of km of granite can produce a small but detectable problem as it releases radon - a radioactive gas, and if you allow it to build up in a modern, well sealed house you can get problems, but I would really doubt that a lump will do you much harm.

In the 1950's they gave the queen a lump of Plutonium in a polyethene bag, to hold and see how warm it was... and she has just got to 80. Bad statistics, and their safety standards were probably a bit lax, but we are a little paranoid these days.
 

Offline realmswalker

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Re: Is volcanic rock more radioactive ?
« Reply #12 on: 20/06/2006 22:55:14 »
what im curious about is whether ancient people (rome, greece, india, south america, etc) ever found radioactive or heat or light emitting elements and rocks and what they thought abut them...
 

Offline Bass

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Re: Is volcanic rock more radioactive ?
« Reply #13 on: 22/06/2006 14:38:55 »
While ancient people may have found radioactive, etc elements- scientists didn't understand radioactivity until relatively recently.

Subduction causes orogeny.
 

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Re: Is volcanic rock more radioactive ?
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