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I was on a beach recently and was contemplating what it would look like if Silicon just didn't bind oxygen very well/at all, perhaps similar to gold.

I'm not sure if something else would take the oxygen's place and create a similar environment to a beach, since silicon is very similar to carbon on the periodic table (Perhaps hydrogen due to its abundance?).

Silicon is also the second most abundant element in Earth's crust and has a high affinity for oxygen.

There need not be any fundamental shift in how chemistry works, perhaps an AI from the first civilization to ever exist in the universe just makes this so by subtly changing physical rules (To the extent such a thing actually exists) in the area in the are to preserve how chemistry normally operated, just minus this one exception.

What exactly would a beach look like since it is mostly composed of SiO_2? Would beaches be more metallic in appearance? Would beaches remain mostly the same, but just with silicon bonded to other elements instead of oxygen?

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

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    $\begingroup$ ...we might not even have a planet upon which to have beaches! A large part of the Earth’s crust is SiO2 $\endgroup$ – Dubukay Jun 30 '18 at 18:07
  • $\begingroup$ That doesn't mean that we wouldn't have a planet. The Si might still be there. I can't know what it would be like without the oxygen though. Even then, out AI might just limit this ti the region within the beaches. $\endgroup$ – Sarah Szabo Jun 30 '18 at 18:14
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    $\begingroup$ "Even then, our AI might limit this to the region within the beaches." The exact implementation details are going to matter here. Done wrong one way, all the beaches freeze over as the AI has to provide bond energy to release the Si from the O. Done wrong another way, you accidentally create an infinite energy machine and destroy the entire universe with it. $\endgroup$ – Cort Ammon Jun 30 '18 at 18:26
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    $\begingroup$ "Hard-science" for a question which starts from the premise that quantum electrodynamics doesn't work? And yet this question was typed on a computer which sent it to a world-spanning network. (Hint: it is indeed possible, almost certain, that there are many laws of physics which are not yet known. On the other hand we are absolutely certain that whatever those laws may be they don't affect the behavior of electrons under ordinary conditions.) $\endgroup$ – AlexP Jun 30 '18 at 20:07
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    $\begingroup$ This is like asking "What would 8 be like if you couldn't add 5 and 3?" $\endgroup$ – Spencer Jun 30 '18 at 21:29
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The answer depends entirely on what magic you use. The answer very well may be grains of silicon, exactly like elemtilas posted. However, It does appear that silicon nitride forms bonds that are more favorable than the silicon-silicon bonds (322kJ/mol rather than 226 kJ/mol), so over time it might undergo that reaction. The process of making silicon nitride is typically done at high temperatures (1850C), so the process may be very slow at room temperature. Fortunately, when we're talking beaches, we can take our time. It's geological scales!

I think the nitrogen bonds are the most likely result. It's another common element, and it's gaseous meaning it will naturally be bathing the silicon grains at all times. There are other silicon compounds out there, such as the silicides, but they bond to a metal, and that may not be a physically favorable reaction because the reagents would not often be in contact.

Of course, we will also have to account for the magic. By this estimate, there's on the order of 700,000,000,000 cubic meters of sand on the world's beaches. At 1602kg/m^3 dry packed, that's 1,121,400,000,000,000kg of sand. Assuming that's primarily SiO2, that's 0.06008kg/mol, thats about 16.6mol/kg, or 18,615,240,000,000,000mol of Silicon Dioxide. At roughly 621kJ/mol of bond energy, that's 11,560,064,040,000,000,000kJ of energy to rip them apart. Taking some zero's off, that's 11,560,064,040TJ, which is on the order of magnitude of "total fossil and nuclear energy sources on the planet."

So my point is, to spend that much energy, someone must have really been fed up with sand in their swim suit!

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  • $\begingroup$ Great answer, I appreciate the humor as well. What state would you expect the Si3N4 appears to be a rather hard material. After a long time on geologic scales what state would the silicon nitride be in? Typical silicon dioxide is very granular but once it enters the field would it form flakes instead of fine grains or some other pattern? $\endgroup$ – Sarah Szabo Jul 1 '18 at 0:01
  • $\begingroup$ @SarahSzabo I don't know enough about the compound to say for sure, but its particular hexagonal pattern (#173) appears to be shared by several compounds which wear gradually rather than fracture. You might see a bunch of particles surrounded by the fine dust of sharp corners that got snapped off. However, the structure also depends on how the oxygen gets taken off of the SI. That's going to be a very invasive process with a lot of energy being thrown around. I think you may be able to use author's discretion regarding what the Si's shape is going into the field $\endgroup$ – Cort Ammon Jul 1 '18 at 0:09
  • $\begingroup$ and I expect the shape of the Si going in will generally not change that much once it nitrates. $\endgroup$ – Cort Ammon Jul 1 '18 at 0:09
  • $\begingroup$ @Sarah Szabo: Typical SiO2 is not granular. It occurs as various-sized crystals in rocks (search for "large quartz crystal" for examples), and as veins in e.g. granite. It's only granular in beaches because it has been broken into pieces by erosion. As I mentioned above, other materials can form sand. (And as a curiousity, I have a roughly softball-sized quartz rock that I picked up from a beach in northern Norway, from a "beach" of similar-sized rocks, so not all "sand" is miniscule grains). $\endgroup$ – jamesqf Jul 1 '18 at 18:53

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