<p>The question "how much" is a little unprecise for geochemical questions. Rather you should think about:</p>

<p>-How much of the element is there per Rock-Volume (=Concentration)?</p>

<p>The crust has a higher U-concentration than the mantle because U is drawn into the minerals that compose the crust. Or you could also say that the minerals that compose the mantle don't like to incorporate U. The same is true for the solid iron core and the iron melt that composes the outer core.</p>

CC BY-SA 3.0
2014-04-17T12:28:40.473Z
For geochemical purposes concentrations are more meaningful than absolute amounts, I suspect that's a comment on the [tag:geochemistry] tag? Because then it's probably more suited as a comment to the question than as part of your answer.
hugovdberg
CC BY-SA 3.0
2014-04-16T10:52:29.130Z
2014-04-16T10:52:29.130Z
tobias47n9e
<p>According to wikipedia, there are around 5.5 million tonnes of <a href="https://en.wikipedia.org/wiki/Uranium#Resources_and_reserves" rel="nofollow noreferrer">uranium in ore deposits</a> that are commercially viable at current prices, and perhaps 35 million tonnes that are potentially viable if prices increase.</p>

<p>Also according to wikipedia, <a href="https://en.wikipedia.org/wiki/Uranium#Biotic_and_abiotic" rel="nofollow noreferrer">the Earth's crust</a> (to 25 km depth) contains an estimated 10^14 tonnes (100 trillion tonnes), while the oceans may contain 10^10 tonnes (10 billion tonnes). This presumably includes the ore figures stated above.</p>

<p>The previous link states that "The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat", however no estimate is given for quantities. Allègre, Lewin and Dupré (1988) state that "The concentration of U in the primordial mantle (bulk Earth) has been determined to be ~21±1 ppb". Back of the envelope calculations would then give us that the <a href="https://en.wikipedia.org/wiki/Mantle_%28geology%29" rel="nofollow noreferrer">mantle</a> is 84% of the <a href="https://en.wikipedia.org/wiki/Earth" rel="nofollow noreferrer">Earth</a> by volume (probably slightly less than that by mass?), and the mass of the earth is 6*10^21 tonnes, which would give us, very approximately, 0.84 * (6*10^21) * (2.1*10^-8) ~= 10^14 tonnes, or roughly the same as is in the Earth's crust.</p>

<ul>
<li>Allègre, C.J., Lewin, E. &amp; Dupré, B., 1988. <a href="https://www.sciencedirect.com/science/article/pii/0009254188900940" rel="nofollow noreferrer">A coherent crust-mantle model for the uranium-thorium-lead isotopic system.</a> 
Chemical Geology, 70(3), pp.211–234. </li>
</ul>

CC BY-SA 3.0
2014-04-16T10:28:54.937Z
I'm not a geologist, but it seems odd to me that the crust would contain as much of such a heavy element as the mantle, considering the latter is 84 times the mass. Might be good if someone feels like double checking these figures. I converted everything to tonnes for consistency, it's possible I miscalculated somewhere.
naught101
CC BY-SA 3.0
2014-04-16T10:35:28.693Z
The reason why the crust has more U than the mantle is because the element is a lithophile element. On a global scale this results in a crust-phile behavior.
tobias47n9e
CC BY-SA 3.0
2014-04-16T10:39:24.083Z
An element that likes being a rock? [Cool](https://en.wikipedia.org/wiki/Goldschmidt_classification#Lithophile_elements)! So I guess my calculation probably isn't too far off the mark...
naught101
CC BY-SA 3.0
2014-04-16T10:44:05.757Z
The nomenclature is a little confusing because the prefix "lith" usually refers to rock and both mantle and crust are made from rock. I think the nomenclature comes from iron smelting where the iron element (siderophile) separate from the rock (lithophile) which roughly corresponds to the Earth's mantle+crust and the Earth's core
tobias47n9e
CC BY-SA 3.0
2014-04-16T10:54:16.910Z
I thought the difference was that the mantle, though it is solid, behaves largely like a very viscous liquid (not a rock), and the crust doesn't? [Lithosphere](https://en.wikipedia.org/wiki/Lithosphere) at least, means only the crust and the very upper, least liquid part of the mantle.
naught101
CC BY-SA 3.0
2014-04-16T11:05:43.390Z
Hope this helps (word limit in comments makes it difficult): The Astenosphere behaves like a liquid but is at all times solid. But from a petrological standpoint the crust (mostly feldspar, quartz) is very different from the mantle (including mantle-lithosphere) which is mostly composed of olivine, pyroxene, hornblende and an Aluminium-mineral. Many elements prefer either the mantle or the crust because of their relation to those minerals. The partitioning of the elements is as far as I know only indirectly influenced by the astenosphere convecting.
tobias47n9e
CC BY-SA 3.0
2014-04-16T13:12:45.660Z
Plate tectonics helps to fractionate all the 'interesting' incompatibles from the mantle - eg. K, REEs, etc.
winwaed
CC BY-SA 3.0
2014-04-16T10:24:21.910Z
2016-12-05T12:18:50.943Z
2016-12-05T12:18:50.943Z
naught101
<p>Are there any estimates of the amount of Uranium there is in Earth's Crust? </p>

<p>From what I know, it's supposed that there are large amounts of Uranium in Earth's Core, the decay of which is responsible for the core maintaining its high temperature. Mining the core is hardly imaginable, while the resources in Crust are more accessible available for mining: so how much is in the Crust, and at what levels of concentration? (which affects the viability of accessing it).</p>

CC BY-SA 3.0
2014-11-04T10:21:29.743Z
Are you talking about accessible uranium or uranium in total? If you are talking about accessible uranium then the concentrations in the crust are not that important but rather how easily the element in concentrated. Take for example the rare earth elements, which are not actually rare. They are just dispersed. On the other hand, gold, which is less abundant readily forms concentrated deposits.
Gimelist
CC BY-SA 3.0
2016-12-11T06:52:09.113Z
The core is comprised of nickel-iron alloy. In a very general sense, heat is generated due to gravity compressing the nickel/iron. As such, nuclear decay isn't thought to be the main source of heat from within the earth. Uranium decay does generate heat in the crust, along with the decay of both Potassium and Thorium which can be harnessed through enhanced geothermal wells, although these three elements are abundant, they are not responsible for the majority of the earths internal heat.
norman_h
CC BY-SA 4.0
2019-02-11T17:08:33.617Z
Note that the radioactive decay heat production in Earth's interior happens mainly in the mantle, the core is unlikely to contain much radioactive material.
Camilo Rada
<resources><uranium><geochemistry>
How much Uranium is there in the Earth's Crust?
Cjxcz Odjcayrwl
# How much Uranium is there in the Earth's Crust?

(Asked by: username_0 on 2014-04-16)

Are there any estimates of the amount of Uranium there is in Earth's Crust?

From what I know, it's supposed that there are large amounts of Uranium in Earth's Core, the decay of which is responsible for the core maintaining its high temperature. Mining the core is hardly imaginable, while the resources in Crust are more accessible available for mining: so how much is in the Crust, and at what levels of concentration? (which affects the viability of accessing it).

**Tags:** resources, uranium, geochemistry

> **Comments:**
> **username_1**: Are you talking about accessible uranium or uranium in total? If you are talking about accessible uranium then the concentrations in the crust are not that important but rather how easily the element in concentrated. Take for example the rare earth elements, which are not actually rare. They are just dispersed. On the other hand, gold, which is less abundant readily forms concentrated deposits.  
> **username_2**: The core is comprised of nickel-iron alloy. In a very general sense, heat is generated due to gravity compressing the nickel/iron. As such, nuclear decay isn't thought to be the main source of heat from within the earth. Uranium decay does generate heat in the crust, along with the decay of both Potassium and Thorium which can be harnessed through enhanced geothermal wells, although these three elements are abundant, they are not responsible for the majority of the earths internal heat.  
> **username_3**: Note that the radioactive decay heat production in Earth's interior happens mainly in the mantle, the core is unlikely to contain much radioactive material.  

---

## 2 answers

### Answer by username_6 on 2014-04-16. Score: 11 | Accepted answer

According to wikipedia, there are around 5.5 million tonnes of [uranium in ore deposits](https://en.wikipedia.org/wiki/Uranium#Resources_and_reserves) that are commercially viable at current prices, and perhaps 35 million tonnes that are potentially viable if prices increase.

Also according to wikipedia, [the Earth's crust](https://en.wikipedia.org/wiki/Uranium#Biotic_and_abiotic) (to 25 km depth) contains an estimated 10^14 tonnes (100 trillion tonnes), while the oceans may contain 10^10 tonnes (10 billion tonnes). This presumably includes the ore figures stated above.

The previous link states that "The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat", however no estimate is given for quantities. Allègre, Lewin and Dupré (1988) state that "The concentration of U in the primordial mantle (bulk Earth) has been determined to be ~21±1 ppb". Back of the envelope calculations would then give us that the [mantle](https://en.wikipedia.org/wiki/Mantle_%28geology%29) is 84% of the [Earth](https://en.wikipedia.org/wiki/Earth) by volume (probably slightly less than that by mass?), and the mass of the earth is 6\*10^21 tonnes, which would give us, very approximately, 0.84 \* (6\*10^21) \* (2.1\*10^-8) ~= 10^14 tonnes, or roughly the same as is in the Earth's crust.

* Allègre, C.J., Lewin, E. & Dupré, B., 1988. [A coherent crust-mantle model for the uranium-thorium-lead isotopic system.](https://www.sciencedirect.com/science/article/pii/0009254188900940)
  Chemical Geology, 70(3), pp.211–234.

> **Comments:**
> **username_6**: I'm not a geologist, but it seems odd to me that the crust would contain as much of such a heavy element as the mantle, considering the latter is 84 times the mass. Might be good if someone feels like double checking these figures. I converted everything to tonnes for consistency, it's possible I miscalculated somewhere.  
> **username_4**: The reason why the crust has more U than the mantle is because the element is a lithophile element. On a global scale this results in a crust-phile behavior.  
> **username_6**: An element that likes being a rock? [Cool](https://en.wikipedia.org/wiki/Goldschmidt_classification#Lithophile_elements)! So I guess my calculation probably isn't too far off the mark...  
> **username_4**: The nomenclature is a little confusing because the prefix "lith" usually refers to rock and both mantle and crust are made from rock. I think the nomenclature comes from iron smelting where the iron element (siderophile) separate from the rock (lithophile) which roughly corresponds to the Earth's mantle+crust and the Earth's core  
> **username_6**: I thought the difference was that the mantle, though it is solid, behaves largely like a very viscous liquid (not a rock), and the crust doesn't? [Lithosphere](https://en.wikipedia.org/wiki/Lithosphere) at least, means only the crust and the very upper, least liquid part of the mantle.  
> **username_4**: Hope this helps (word limit in comments makes it difficult): The Astenosphere behaves like a liquid but is at all times solid. But from a petrological standpoint the crust (mostly feldspar, quartz) is very different from the mantle (including mantle-lithosphere) which is mostly composed of olivine, pyroxene, hornblende and an Aluminium-mineral. Many elements prefer either the mantle or the crust because of their relation to those minerals. The partitioning of the elements is as far as I know only indirectly influenced by the astenosphere convecting.  
> **username_7**: Plate tectonics helps to fractionate all the 'interesting' incompatibles from the mantle - eg. K, REEs, etc.  

---

### Answer by username_4 on 2014-04-16. Score: 5

The question "how much" is a little unprecise for geochemical questions. Rather you should think about:

-How much of the element is there per Rock-Volume (=Concentration)?

The crust has a higher U-concentration than the mantle because U is drawn into the minerals that compose the crust. Or you could also say that the minerals that compose the mantle don't like to incorporate U. The same is true for the solid iron core and the iron melt that composes the outer core.

> **Comments:**
> **username_5**: For geochemical purposes concentrations are more meaningful than absolute amounts, I suspect that's a comment on the [tag:geochemistry] tag? Because then it's probably more suited as a comment to the question than as part of your answer.  

---

