Question definitions:

"safely" - the metal would be strictly beneficial; there would be no health problems caused by it (perhaps at least for most, there may be "birth defects" which cause some of the population reject it. I'm not set on that idea though).

"functional" - I mean to use as strength enhancement/armor. Preferably, it would be enough to drastically slow a bullet, reducing the damage caused.

"metal" - I was thinking about iron, such as a beavers teeth. However, if you can justify something else, then by all means.


This question is merely asking how much more metal (pure or compound) a creature would need to be able to resist a bullet, or stop sword. would that concentration be unhealthy to life as we know it?

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    $\begingroup$ Calcium is a metal. We deposit a lot of it in our bones. It's perfectly safe. If you are not satisfied with it, remove "However, if you can justify something else, then by all means." and just stick to the iron. $\endgroup$ – Mołot May 25 '18 at 6:46
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    $\begingroup$ @Mołot: But the calcium in bones is in the form of calcium phosphate, which is non-metallic. For an actual metal that will work as a bone substitute,try titanium. It is widely used for medical implants: en.wikipedia.org/wiki/Titanium_biocompatibility $\endgroup$ – jamesqf May 25 '18 at 6:50
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    $\begingroup$ Why not add some titanium? Isn't that the current go to metal because it doesn't react too much with anything and our body doesn't just straight up reject it? $\endgroup$ – Shadowzee May 25 '18 at 7:03
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    $\begingroup$ @Aethenosity I'm not sure how accurate this would be scientifically, but maybe they can have carbon fibre like skin? I could imagine it operating like how our skin currently works with many layers and flaking away. I'm not sure how you could form carbon fibre naturally. There is also a sea snail I think which can form a part of its body out of iron which researchers were looking into, to try and duplicate, so you could use that for iron skin. $\endgroup$ – Shadowzee May 25 '18 at 7:09
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    $\begingroup$ @Mołot: As I read the question, the OP is asking for actual metal - stuff that's "hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity" - not compounds that contain metallic elements. (Of which we have a number already.) The metal could be pure, or an alloy such as bronze or steel. $\endgroup$ – jamesqf May 25 '18 at 19:22

Maybe your issue here is more a problem of weight and availability instead of a problem of health.
A way to protect health would be a cyst around each zone with metal, so that might not be a problem.
About the weight. Let's imagine we select iron (poor choice because it rusts, but just as an example). Iron density is close to 7800 kg/m3. So a plate of 5mm of iron (enough for your purpose) of 1 m3 would have a weight of 39.4 kg. Human skin has 2 m2 of surface, so you would need almost 80 kg of iron or its equivalent to cover the body. Other metals can be used, but the weight might be similar.
Maybe your creature can keep those 80 kg extra.

But here is the main issue:
¿From where that creature is going to absorb that amount of metal?
¿How that metal is going to form a crystal in absence of high temperature? After all, a plate of metal requires high temperature to be formed. Otherwise it would be only a bunch of separated atoms.

Hence, what you need is a polymer or a compound instead of a pure metal. Something that can be synthetized at lower temperatures; natural examples are spider silk, tooth enamel, silk or lignin.

  • $\begingroup$ An extra 80kg will also be difficult for horses to carry - the age of war-chariots will endure. $\endgroup$ – user535733 May 29 '18 at 18:53

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