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On a world similar to Earth in many aspects, a species exists that is partly carbon-based and partly X-based. X can (mostly) be found in the thick exoskeleton that this creature possesses. I'm looking for what kind of compound X might be that is scientifically plausible. The exoskeleton should have the following properties:

  • Good electrical conductivity on the 'inside', electrically isolating on the 'outside' (possibly multiple layers)
  • Heat and fire resistant
  • (Somewhat) difficult to penetrate with regular means (like knives, bullets)
  • Flexible enough to allow movement
  • Rigid enough to allow structural integrity without an endoskeleton
  • Needs to be shed / regrown (moulting)
  • Should allow heat transfer (for creature to lose heat)
  • Should be able to occur in an Earth-like environment (see also below)

As I understand it, a silicon structure can resist high temperatures and is quite stable with regards to chemical reactions, which are good properties for a natural defensive shell/armour that this creature needs. But I'm not sure if silicon meets enough of the above.

I understand that this is a rather long 'wish list'. If there is a compound that covers most of these, I would also really like to hear about it! (and what the flaws are) Maybe a combination of compounds or just different layers made up of different substances might work as well. X might also be something carbon-based, if that is applicable, or something that does not exist / has not been discovered, but is plausible to exist.

Edit: moved some questions to be asked later.

Interesting threads regarding silicon on Worldbuilding:

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    $\begingroup$ (1) move healing, and everything else you possibly can) to another question later. Too many questions get you put on hold as "too broad." (2) You have a lot of opposites: (a) flexible but rigid, (b) thermally insulative but thermally conductive (thermally polarized), (c) electrically conductive but electrically insulative (electrically planar). It's a tall order, but this site has regularly suprised me. $\endgroup$ – JBH Oct 24 '17 at 23:54
  • $\begingroup$ Century, per John's answer below, I think it won't be too hard to satisfy what you want. The big deal you have to worry about is the size of your creatures (if that's a factor; it might be interesting to have a whole civilization of tiny critters). Scaling up to bigness appears to be exoskeletal creatures Achilles' heel, though warm temps, humidity, and increased O2 in the air seem to help: wired.com/2010/11/huge-dragonflies-oxygen $\endgroup$ – akaioi Oct 25 '17 at 2:38
  • $\begingroup$ I've removed the questions to ask later when I've decided what it will be :) Those questions are the ones I want an answer to, but I had to start at what the exoskeleton actually consists of. @akaioi: the creatures are somewhat bigger than a big dog. So nothing special there. $\endgroup$ – Century Oct 25 '17 at 7:40
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Chitin, keratin, and wood all fulfill all of those requirements so you don't need anything special. They are all composites and like all composites the properties can change across the material as the composition changes.

The only one that will give you any trouble is electrical conductivity, but flesh being mostly made of water has good electrical conductivity so whatever is inside the exoskeleton will conduct electricity just fine.

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  • $\begingroup$ Creatures with wooden shells or exoskeletons! I like it! The OP's description of what he wants sounds like 'skin'. Very strong skin. Keratin is a major component of skin. Plus one for the bark-covered beasties and for stretching my mind in directions it didn't expect to go. $\endgroup$ – a4android Oct 25 '17 at 3:13
  • $\begingroup$ Would you suggest I let this question 'be' and move on to a new question, picking an option for the skeleton and asking my other questions about the life style of this creature and its vulnerabilities there? $\endgroup$ – Century Oct 25 '17 at 8:16
  • $\begingroup$ that would be best, keep in mind if you use chitin you can look at insects and shellfish for comparison with the other two you are looking at more theoretical approach. . $\endgroup$ – John Oct 25 '17 at 14:20
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The first thought that comes to mind is fish - they live in an environment where they have no option but to ingest whatever substance is around them as they breathe. The ocean is rich in minerals, and fish solve this problem by moving excessive or harmful substances to their skins, which is what that metallic under-skin is.

So your creatures might have started life in the oceans, and not only developed this mechanism for moving the minerals to their skin, but also evolved it into a good survival technique. After moving to land living they were forced to find this substance or substances in soil, for example, to maintain this protective layer.

Having this substance "grown" as part of the skin would probably allow some flexibility, though the creatures would also have evolved to dissolve the substance somehow into a form that their bodies could manipulate.

Rigidity could be provided by a setup similar to snake scales, coupled with very strong musculature though that would probably have to connect to something, so you may need to include at least a spine.

I think @John has the right idea regarding conductivity - the substance can be electrically non-conductive, while the substance of the body is somewhat conductive.

Any substance build in a thick or intricate enough layer should offer at least some protection against penetrating objects.

The only substance I know of off the top of my head (and which is also terribly bad for life) that is heat and fire resistant is asbestos. Not sure whether that would be found in an ocean, though. Asbestos is also a fibrous mineral, come to think of it, so might be very suitable, once you iron out all the details.

If the creatures are constantly ingesting this substance (compulsively), their outer layer would be constantly growing, and in order for the body to maintain the right balance of flexibility versus rigidity, some of it would have to sloughed off at intervals. If the creature is scaly, they might also shed scales individually, from time to time, the way we shed hair.

If the creature were scaly, and able to shift or lift the scales, doing so would allow their bodies to vent heat through the openings. Of course, such an action would make the creature more vulnerable to attack.

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