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I am currently building a planet that weighs about 4 earth masses and is 2.3 earth radii long. It is an ammonia planet (as the title suggests), and has ammonia oceans with some dissolved water ice, methanol and salts (sodium, chlorides, sulfates, potassium etc.). The average temperature is about 260ºK on the planet and the avg pressure at sea level is about 2.5 atm.

It has an ocean with the following composition:

  • Ammonia: 80%
  • Ice: 12% (which sinks under the ammonia and is mostly regular ice, but at very deep places, it may become ice III)
  • Salts: 5.5%
  • Ethanol: 2%
  • Other: 0.5%

If you can't already tell, this solution is quite basic, so basic that a lot of common minerals that we have in our crust would simply dissolve. As a result, I would like to understand what minerals/compounds would be able to survive the fierce chemical weathering and make up the continental and oceanic crust. If you give percentages, that would be great.

Thanks in advance.

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  • $\begingroup$ Ammonia is a solvent, just like water. Ammonia simply dissolves the dissolvable faster than water will. But it still takes a lot of time to dissolve rock. I've never found ammonia-based biology believable due to how quickly it can dissolve bonds, but ignoring the organic component, the crust of Earth would be more than suitable as a model for your ammonia planet. If you want to test the theory, fill a mason jar half full of dirt and fill the rest with ammonia. Close the lid (to simulate a non-oxygen-based atmosphere) and wait a few weeks. Drain, dry, and look at the dirt that's still there. $\endgroup$
    – JBH
    Mar 23 at 2:03
  • $\begingroup$ Understood and agreed. The only issue with your theory is that over millions of years, all that ammonia is definitely going to dissolve at least some significant amount of stuff. That's why I asked this question, and I'm not able to find any resources on what/how much minerals dissolve in an ammonia/ice mixture (with some other stuff). $\endgroup$
    – Neil Iyer
    Mar 23 at 5:50
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    $\begingroup$ I would say volcanic activities make this a non issue as generally new crust is always forming. What i think is more of a problem is that the ammonia ocean may just dry up over time. The most probable way to avoid this maybe to have some highly resistant layer but Ii have no idea how it would form naturally. $\endgroup$ Mar 23 at 15:20
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    $\begingroup$ @Fallenspacerock makes an excellent point about volcanism. It's why, after millions of years, water hasn't worn our world down to nothing. In other words, your world need only more volcanic to solve the problem. This lets you craft the crust based on Earth's with shifts in percentages to meet your world's needs. $\endgroup$
    – JBH
    Mar 23 at 17:43
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    $\begingroup$ @Fallenspacerock Understood. I just need more volcanic activity to make sure that the crust doesn't fizz away and it can probably be just like earth's. What can I do about the ocean dissolving (that wouldn't be very good). $\endgroup$
    – Neil Iyer
    Mar 23 at 19:06

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