<p>I have no knowledge of the quantified specifics, but would like to point out two effects that may be relevant:</p>
<ul>
<li>We already exploited the easiest precious metal deposits on <em>the top of</em> Earth's crust to the extent that we could find and access them. This goes back millenia and intensified in recent centuries. Modern Earth is not natural.</li>
<li>Asteroids can be cherry-picked. You want to mine the freak asteroid, not the normal asteroid.</li>
</ul>

CC BY-SA 4.0
2022-06-10T18:30:02.270Z
2022-06-10T18:30:02.270Z
Emilio M Bumachar
<p>This is in part marketing hype by wanna-be asteroid mining companies. That said, some asteroids are suspected to be richer in precious metals than is the Earth's crust. For example, the Earth's crust is significantly depleted in gold compared to the solar system as a whole. I wrote about the reasons why this is the case at <a href="https://physics.stackexchange.com/a/144775/52112">physics.stackexchange.com</a>.</p>
<p>Gold and related precious metals are siderophiles, which means &quot;iron-loving&quot;. When the Earth differentiated, the iron and nickel that sank to the center of the Earth took other siderophiles with them. In a sense, the precious metals are more siderophilic than is iron itself. Gold et al. easily dissolve in molten iron. Precious metals are so chemically inert that they do not readily combine form compounds with other elements.</p>
<p>There is a lot more gold and other precious metals in the Earth's core than there is in all of the asteroids combined.</p>

CC BY-SA 4.0
2022-06-09T20:20:15.250Z
So it sounds iron-nickel asteroids are the ones suspected to have more gold in them? What about other elements that, while not necessarily precious, are still rare and expensive, like tantalum and iridium?
zucculent
CC BY-SA 4.0
2022-06-09T20:46:05.567Z
@zucculent Correct (regarding iron-nickel asteroids.) The cost involved in sending mining and smelting equipment to an asteroid and bringing the mined metals back to Earth overwhelms the value of those precious metals. (That ignores that doing so is TRL-3 at best.) Asteroid mining, if it ever does become commercial, will initially focus on boring substances such as water and methane, and using those materials in space. The cost of sending a kilogram of water into orbit exceeds the value of a kilogram of gold mined on the Earth.
David Hammen
CC BY-SA 4.0
2022-06-09T21:05:46.030Z
I'm not really interested in the concept of bringing all the mined minerals back to Earth. I agree that it's far from being practical, if it ever will be practical. I'm just interested in knowing the concentration of rare and expensive metals in those asteroids compared to Earth's crust.
zucculent
CC BY-SA 4.0
2022-06-09T22:32:54.837Z
@zucculent Some asteroids were large enough and hot enough to have differentiated. The isotope $^{26}\text{Al}$ (aluminum-26), with a half life of 717,000 years, is widely hypothesized to have provided significant additional heating during the formation of the solar system. Massive collisions later cracked some of those differentiated asteroids into parts. Many, many parts.
David Hammen
CC BY-SA 4.0
2022-06-09T23:09:05.407Z
Here's a periodic table: https://en.wikipedia.org/wiki/Goldschmidt_classification
PM 2Ring
CC BY-SA 4.0
2022-06-09T23:24:54.020Z
So are the siderophilic elements the only ones we'd find in much higher concentrations in certain asteroids, since the Earth's crust has plenty of rock and (I imagine) chalcogen ores?
zucculent
CC BY-SA 4.0
2022-06-10T18:39:13.887Z
@DavidHammen: You are way off! A kilo of gold costs about $60,000; putting a kilo of water into orbit on a Falcon 9 can be done for [about $4,000](https://www.reddit.com/r/SpaceXLounge/comments/td8fv9/falcon_9_price_per_kilogram_to_leo/).
TonyK
CC BY-SA 4.0
2022-06-12T08:07:56.627Z
@TonyK That's the cost to send something to LEO. The water will need to be stored in a container, which has mass. Something a bit stronger and hence more massive than a milk jug will be needed. Besides, LEO is not where the interesting sci-fi level space construction will occur. It will be a construction depot in a pseudo-orbit about one of the Earth-Moon Lagrange points. Sending water in a container from the Earth to such a depot will cost a whole lot more than $4000/kg, even after taking into account how disruptive SpaceX has been.
David Hammen
CC BY-SA 4.0
2022-06-13T14:57:29.627Z
Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/137050/discussion-on-answer-by-david-hammen-why-are-asteroids-so-much-richer-in-preciou).
called2voyage
CC BY-SA 4.0
2022-06-09T19:57:03.293Z
2022-06-09T19:57:03.293Z
David Hammen
<p>Did the majority of Earth's precious metals sink below the crust during Earth's formation?</p>

CC BY-SA 4.0
2022-06-10T04:15:18.070Z
https://en.wikipedia.org/wiki/Asteroid_mining
Nilay Ghosh
CC BY-SA 4.0
2022-06-10T17:08:41.140Z
There's an observation selection bias inherent in your question.  Those metals are "precious" *because* they're rare in earth's crust.  If gold were abundant, we'd be making mundane things like paperclips and beverage cans out of it, and never even consider mining asteroids for it.
dan04
CC BY-SA 4.0
2022-06-10T22:31:22.050Z
@dan04 I agree with you, but your examples are bad because gold would not be appropriate for those applications. I think a better example would be [golden showers](https://www.youtube.com/watch?v=nwo8m-m0VQg).
Christopher Schultz
CC BY-SA 4.0
2022-06-11T04:01:38.783Z
@ChristopherSchultz Gold-based alloys, then? And for electrical wiring, too?
Rosie F
CC BY-SA 4.0
2022-06-11T04:31:29.890Z
It would be good to give the motivation of the question.  The accepted answer assumes you are interested in asteroid mining.  Another reason for the same question would be to understand the significance of the layer between the Cretaceous and Tertiary periods being enriched in iridium and whether that is good evidence for an asteroid impact.  Those deserve very different answers.  Fundamentally, the answer is yes.  Is that sufficient?
Ross Millikan
CC BY-SA 4.0
2022-06-11T16:43:34.297Z
@RosieF Gold is really quite useless for virtually any practical application at all until your civilization's technology level reaches electronics.  Gold is an amazing conductor, not as good as silver but unlike silver it doesn't tarnish.  It doesn't make for good electrical wiring because of its weight, but for electronics where tiny trace wires are needed, it's ideal.  Before that, gold is practically useless for literally anything other than looking pretty.
Mason Wheeler
CC BY-SA 4.0
2022-06-12T11:36:04.860Z
@MasonWheeler copper is a better conductor than gold, 5.8E7 instead of 4.8E7 S/m. But gold is used in a very thin layer to protect the surface of copper conductors against oxidation. Tiny traces are possible with copper or aluminum. Connectors are plated with gold to get a lower contact resistance by protecting the copper below against oxidation. HF parts are plated with gold due to the skin effect, the current concentrates close to the surface, therefore the surface should be free from copper oxide.
Uwe
CC BY-SA 4.0
2022-06-12T11:36:30.953Z
"Precious" is relative.  When/if we actually start doing any asteroid mining or living in space, water, methane and similar mundane substances could well prove more valuable than many precious metals as we'll need fuel and food.  A ton of gold versus a ton of water might be a very easy choice - grab the water, leave the useless gold. :-)
StephenG - Help Ukraine
CC BY-SA 4.0
2022-06-12T13:10:26.300Z
@Uwe So yeah, what I said above.  Gold is an amazing conductor, not as good as silver *or copper* but unlike silver *or copper* it doesn't tarnish.
Mason Wheeler
<asteroids>
Why are asteroids so much richer in precious metals than Earth's crust?
zucculent
# Why are asteroids so much richer in precious metals than Earth's crust?

(Asked by: username_0 on 2022-06-09)

Did the majority of Earth's precious metals sink below the crust during Earth's formation?

**Tags:** asteroids
> **Comments:**
> **username_1**: https://en.wikipedia.org/wiki/Asteroid_mining  
> **username_2**: There's an observation selection bias inherent in your question.  Those metals are "precious" *because* they're rare in earth's crust.  If gold were abundant, we'd be making mundane things like paperclips and beverage cans out of it, and never even consider mining asteroids for it.  
> **username_3**: @dan04 I agree with you, but your examples are bad because gold would not be appropriate for those applications. I think a better example would be [golden showers](https://www.youtube.com/watch?v=nwo8m-m0VQg).  
> **username_4**: @ChristopherSchultz Gold-based alloys, then? And for electrical wiring, too?  
> **username_5**: It would be good to give the motivation of the question.  The accepted answer assumes you are interested in asteroid mining.  Another reason for the same question would be to understand the significance of the layer between the Cretaceous and Tertiary periods being enriched in iridium and whether that is good evidence for an asteroid impact.  Those deserve very different answers.  Fundamentally, the answer is yes.  Is that sufficient?  
> **username_6**: @RosieF Gold is really quite useless for virtually any practical application at all until your civilization's technology level reaches electronics.  Gold is an amazing conductor, not as good as silver but unlike silver it doesn't tarnish.  It doesn't make for good electrical wiring because of its weight, but for electronics where tiny trace wires are needed, it's ideal.  Before that, gold is practically useless for literally anything other than looking pretty.  
> **username_7**: @MasonWheeler copper is a better conductor than gold, 5.8E7 instead of 4.8E7 S/m. But gold is used in a very thin layer to protect the surface of copper conductors against oxidation. Tiny traces are possible with copper or aluminum. Connectors are plated with gold to get a lower contact resistance by protecting the copper below against oxidation. HF parts are plated with gold due to the skin effect, the current concentrates close to the surface, therefore the surface should be free from copper oxide.  
> **username_8**: "Precious" is relative.  When/if we actually start doing any asteroid mining or living in space, water, methane and similar mundane substances could well prove more valuable than many precious metals as we'll need fuel and food.  A ton of gold versus a ton of water might be a very easy choice - grab the water, leave the useless gold. :-)  
> **username_6**: @Uwe So yeah, what I said above.  Gold is an amazing conductor, not as good as silver *or copper* but unlike silver *or copper* it doesn't tarnish.  

---

## 2 answers

### Answer by username_10 on 2022-06-09. Score: 31 | Accepted answer

This is in part marketing hype by wanna-be asteroid mining companies. That said, some asteroids are suspected to be richer in precious metals than is the Earth's crust. For example, the Earth's crust is significantly depleted in gold compared to the solar system as a whole. I wrote about the reasons why this is the case at [physics.stackexchange.com](https://physics.stackexchange.com/a/144775/52112).

Gold and related precious metals are siderophiles, which means "iron-loving". When the Earth differentiated, the iron and nickel that sank to the center of the Earth took other siderophiles with them. In a sense, the precious metals are more siderophilic than is iron itself. Gold et al. easily dissolve in molten iron. Precious metals are so chemically inert that they do not readily combine form compounds with other elements.

There is a lot more gold and other precious metals in the Earth's core than there is in all of the asteroids combined.

> **Comments:**
> **username_0**: So it sounds iron-nickel asteroids are the ones suspected to have more gold in them? What about other elements that, while not necessarily precious, are still rare and expensive, like tantalum and iridium?  
> **username_10**: @zucculent Correct (regarding iron-nickel asteroids.) The cost involved in sending mining and smelting equipment to an asteroid and bringing the mined metals back to Earth overwhelms the value of those precious metals. (That ignores that doing so is TRL-3 at best.) Asteroid mining, if it ever does become commercial, will initially focus on boring substances such as water and methane, and using those materials in space. The cost of sending a kilogram of water into orbit exceeds the value of a kilogram of gold mined on the Earth.  
> **username_0**: I'm not really interested in the concept of bringing all the mined minerals back to Earth. I agree that it's far from being practical, if it ever will be practical. I'm just interested in knowing the concentration of rare and expensive metals in those asteroids compared to Earth's crust.  
> **username_10**: @zucculent Some asteroids were large enough and hot enough to have differentiated. The isotope $^{26}\text{Al}$ (aluminum-26), with a half life of 717,000 years, is widely hypothesized to have provided significant additional heating during the formation of the solar system. Massive collisions later cracked some of those differentiated asteroids into parts. Many, many parts.  
> **username_11**: Here's a periodic table: https://en.wikipedia.org/wiki/Goldschmidt_classification  
> **username_0**: So are the siderophilic elements the only ones we'd find in much higher concentrations in certain asteroids, since the Earth's crust has plenty of rock and (I imagine) chalcogen ores?  
> **username_12**: @DavidHammen: You are way off! A kilo of gold costs about $60,000; putting a kilo of water into orbit on a Falcon 9 can be done for [about $4,000](https://www.reddit.com/r/SpaceXLounge/comments/td8fv9/falcon_9_price_per_kilogram_to_leo/).  
> **username_10**: @TonyK That's the cost to send something to LEO. The water will need to be stored in a container, which has mass. Something a bit stronger and hence more massive than a milk jug will be needed. Besides, LEO is not where the interesting sci-fi level space construction will occur. It will be a construction depot in a pseudo-orbit about one of the Earth-Moon Lagrange points. Sending water in a container from the Earth to such a depot will cost a whole lot more than $4000/kg, even after taking into account how disruptive SpaceX has been.  
> **username_13**: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/137050/discussion-on-answer-by-david-hammen-why-are-asteroids-so-much-richer-in-preciou).  

---

### Answer by username_9 on 2022-06-10. Score: 4

I have no knowledge of the quantified specifics, but would like to point out two effects that may be relevant:

* We already exploited the easiest precious metal deposits on *the top of* Earth's crust to the extent that we could find and access them. This goes back millenia and intensified in recent centuries. Modern Earth is not natural.
* Asteroids can be cherry-picked. You want to mine the freak asteroid, not the normal asteroid.


---

