<p>Within our <a href="https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe" rel="nofollow noreferrer">solar system the least abundant</a>, stable and non radioactive element is <a href="https://en.wikipedia.org/wiki/Tantalum" rel="nofollow noreferrer">Tantalum</a>, atomic number 73.</p>
<p>Its chemical inertness,</p>
<blockquote>
<p>make it valuable for laboratory and industrial equipment such as reaction vessels and vacuum furnaces</p>
</blockquote>
<p>Back in the 1970s and 1980s it was popular to make <a href="https://en.wikipedia.org/wiki/Tantalum_capacitor" rel="nofollow noreferrer">electronic capacitors</a> using tantalum because they were smaller in size than the electronic capacitors that were made previously. This made them popular for use in hand held calculators and other similar small electronic devices.</p>
<blockquote>
<p>Tantalum is dark (blue-gray), dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids.</p>
</blockquote>
<p>Element 43, <a href="https://en.wikipedia.org/wiki/Technetium" rel="nofollow noreferrer">Technetium</a>, is very rare, radioactive and has a short half life. On Earth it is a synthetic material and wouldn't be suitable for your purposes.</p>
<p>Similarly, <a href="https://en.wikipedia.org/wiki/Promethium" rel="nofollow noreferrer">Promethium</a>, element 61, is rare, but radioactive. The same applies for elements 84 through to 89.</p>

CC BY-SA 4.0
2023-04-11T18:07:54.043Z
"Back in the 1970s and 1980s it was popular to make electronic capacitors using tantalum"...and in the 1990s, and 2000s, and 2010s, and 2020s...
Christopher James Huff
CC BY-SA 4.0
2023-04-11T23:45:37.553Z
It also has a stable nuclear isomer, Ta180m with an abundance of 0.01201(8)%.
Anders Sandberg
CC BY-SA 4.0
2023-04-12T02:04:56.453Z
This source image will be useful: https://commons.wikimedia.org/wiki/File:Element-haeufigkeit.svg
Nilay Ghosh
CC BY-SA 4.0
2023-04-12T02:28:55.567Z
It looks like Tantalum will be a logical choice for me. It's incredibly rare and has industrial uses.  Thank you all for your expertise! 
In the future I will be asking in worldbuilding
Dylan Bozarth
CC BY-SA 4.0
2023-04-11T05:07:29.180Z
2023-04-11T05:07:29.180Z
Fred
<p>I am making a hard sci-fi game with a focus on realism, in this game there is a need for a hard element to base money off of. Similar to how gold is used on earth.
<br />
I know there are lots of elements that only exist for seconds at a time that are technically <em>rare</em> but wouldn't work as a currency. What element in the universe would aliens be most likely to be trading back and forth?</p>

CC BY-SA 4.0
2023-04-11T03:28:15.330Z
*Welcome to Astronomy SE!* This is a challenging question. You'll have to work harder to define "stable". if something has a half-life longer than the age of the universe, will you call it unstable? If it's radioactive decay rate is so small that it's almost undetectable, is that still unstable? Also, I think you can drop "in the universe" because as far as I know there aren't "stable" elements that are known to be in the universe that are not made or isolated right here on Earth. I don't think "in the universe" helps the title or the question, it's a distraction.
uhoh
CC BY-SA 4.0
2023-04-11T03:30:06.127Z
I guess adding "in the universe" helps to make this more likely to be seen as possibly on-topic here in Astronomy. Chemistry SE and Physics SE are more appropriate sites
uhoh
CC BY-SA 4.0
2023-04-11T08:01:34.303Z
Please note [worldbuilding.se] where they do handle questions like this but also provide answers which may be more helpful when building a fictional setting.  For example extremely rare elements do not necessarily make a good basis for a currency, something they might give advice on there, but we won't here.
StephenG - Help Ukraine
CC BY-SA 4.0
2023-04-11T08:24:51.653Z
I'd vote to migrate to Worldbuilding
Rory Alsop
CC BY-SA 4.0
2023-04-11T09:05:10.910Z
We don't base our currencies on gold any more. See https://en.wikipedia.org/wiki/Gold_standard Why not use something useful, like energy?
PM 2Ring
CC BY-SA 4.0
2023-04-11T17:01:17.140Z
@PM 2Ring   Gold is not used as a base of currencies.  But possibly aliens societies not as advanced as 21st century Earth might still use gold or some other rare element as the basis of their currencies.
M. A. Golding
CC BY-SA 4.0
2023-04-11T18:15:24.007Z
@M.A.Golding Maybe, but I'm assuming that the OP's game involves interstellar trading, so the aliens *are* more advanced than us. Perhaps they use rocket fuel as a currency basis, eg deuterium. Or anti-hydrogen...
PM 2Ring
<observable-universe>
What is the rarest stable element in the universe?
Dylan Bozarth
# What is the rarest stable element in the universe?

(Asked by: username_0 on 2023-04-11)

I am making a hard sci-fi game with a focus on realism, in this game there is a need for a hard element to base money off of. Similar to how gold is used on earth.
  
I know there are lots of elements that only exist for seconds at a time that are technically *rare* but wouldn't work as a currency. What element in the universe would aliens be most likely to be trading back and forth?

**Tags:** observable-universe

> **Comments:**
> **username_1**: *Welcome to Astronomy SE!* This is a challenging question. You'll have to work harder to define "stable". if something has a half-life longer than the age of the universe, will you call it unstable? If it's radioactive decay rate is so small that it's almost undetectable, is that still unstable? Also, I think you can drop "in the universe" because as far as I know there aren't "stable" elements that are known to be in the universe that are not made or isolated right here on Earth. I don't think "in the universe" helps the title or the question, it's a distraction.  
> **username_1**: I guess adding "in the universe" helps to make this more likely to be seen as possibly on-topic here in Astronomy. Chemistry SE and Physics SE are more appropriate sites  
> **username_2**: Please note [worldbuilding.se] where they do handle questions like this but also provide answers which may be more helpful when building a fictional setting.  For example extremely rare elements do not necessarily make a good basis for a currency, something they might give advice on there, but we won't here.  
> **username_3**: I'd vote to migrate to Worldbuilding  
> **username_4**: We don't base our currencies on gold any more. See https://en.wikipedia.org/wiki/Gold_standard Why not use something useful, like energy?  
> **username_5**: @username_4   Gold is not used as a base of currencies.  But possibly aliens societies not as advanced as 21st century Earth might still use gold or some other rare element as the basis of their currencies.  
> **username_4**: @M.A.Golding Maybe, but I'm assuming that the OP's game involves interstellar trading, so the aliens *are* more advanced than us. Perhaps they use rocket fuel as a currency basis, eg deuterium. Or anti-hydrogen...  

---

## 1 answers

### Answer by username_6 on 2023-04-11. Score: 4 | Accepted answer

Within our [solar system the least abundant](https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Universe), stable and non radioactive element is [Tantalum](https://en.wikipedia.org/wiki/Tantalum), atomic number 73.

Its chemical inertness,

> make it valuable for laboratory and industrial equipment such as reaction vessels and vacuum furnaces

Back in the 1970s and 1980s it was popular to make [electronic capacitors](https://en.wikipedia.org/wiki/Tantalum_capacitor) using tantalum because they were smaller in size than the electronic capacitors that were made previously. This made them popular for use in hand held calculators and other similar small electronic devices.

> Tantalum is dark (blue-gray), dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids.

Element 43, [Technetium](https://en.wikipedia.org/wiki/Technetium), is very rare, radioactive and has a short half life. On Earth it is a synthetic material and wouldn't be suitable for your purposes.

Similarly, [Promethium](https://en.wikipedia.org/wiki/Promethium), element 61, is rare, but radioactive. The same applies for elements 84 through to 89.

> **Comments:**
> **username_7**: "Back in the 1970s and 1980s it was popular to make electronic capacitors using tantalum"...and in the 1990s, and 2000s, and 2010s, and 2020s...  
> **username_8**: It also has a stable nuclear isomer, Ta180m with an abundance of 0.01201(8)%.  
> **username_9**: This source image will be useful: https://commons.wikimedia.org/wiki/File:Element-haeufigkeit.svg  
> **username_0**: It looks like Tantalum will be a logical choice for me. It's incredibly rare and has industrial uses.  Thank you all for your expertise!  In the future I will be asking in worldbuilding  

---

