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Human ingenuity has made great use of metal tools. But are there any known, or potential, biological processes that might produce sizable solid metal objects like how for example skeletons and shells are being grown? Does solid metal manufacturing require melting point temperatures beyond what biological processes can survive, or could it be grown by proteins more or less atom by atom?

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    $\begingroup$ i think that, even if it could be possible to "be grown by proteins more or less atom by atom", there would be two problems. First, metals are already hard to find in a proper manner for consumption, and even if it was easy, in excess they become toxic to the organism. Second, building something like a metal skeleton would mean a great loss in adaptability, as once made, I understand it would be immensely difficult to unmake without using great amounts of energy. So I don't see how metal parts could be biologically used apart from beings with a somewhat developed intelligence and means $\endgroup$ – Filipe Rocha Apr 10 '17 at 15:12
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    $\begingroup$ You might have better luck on worldbuilding.stackexchange.com if this is for a story. They are more focused on finding ways to make something sound feasible if that is what you're looking for. I'm not giving an opinion either way on if it should be here. That depends on your intention. $\endgroup$ – Paul S Apr 11 '17 at 16:13
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That is an excellent question. I was a little confused at first because, without realizing it, you actually cited a perfect example of a biological process that manipulates metal: bone formation.

Bone is made of hydroxyapatite crystal, which is a mineral whose main ingredient is, of course, calcium (metal).

Now, to answer the how of your question; bone is formed, as you eluded, through protein to protein interaction mediated by cells called osteoblasts (osteo- = bone, -blast = immature cell). The osteoblast first locates a site on the bone that is to be expanded, then encases itself in a framework of collagen fibers. When this is done, calcium phosphate and hydroxide bind to the collagen and "harden" as hydroxyapatite (Ca10(PO4)6(OH)2). The osteoblast, now encased in a shell of hydroxyapatite (called the lacuna), transforms into an osteocyte (-cyte = mature cell) and projects long arm-like structures called filopodia which it uses as sensors and to communicate with surrounding osteocytes. All that adds up to look an awful lot like this (with respect to the fact that they are usually fully enclosed, but that would make for quite an insipid picture):

enter image description here

Finally, to put Filipe Rocha's concerns to rest, how is this fully organic and (almost) solid metal structure adapted and "unmade," should the need arise? Well, there is a third type of bone cell called an osteoclast (-clast = to break). Osteoclasts break down bone by secreting hydrogen ions to dissolve the calcium in hydroxyapatite, then cathepsin and other protease to digest the collagen network.

So there you go; a fully biological system with the capability to not only create a non-toxic, solid metal structure, but also maintain it and even manipulate and "unmake" it. Even though bone is not an organ, I'm sure this system could be modified for such an implement if we put our minds to it... :)

Edit: If calcium isn't "metally" enough for you, you might want to check out limpet teeth, which are comprised of goethite, iron oxide-hydroxide (FeO(OH)). I can go further in depth with the biological processes necessary to produce this mineral if you want; just ask. :)

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    $\begingroup$ I did think about bone, but did not include it because Calcium is not a true metal. It is actually an alkaline earth metal, and its properties are somewhat different from true metals. I was going to suggest bone as being an almost perfect example of a biological process that manipulates metal, but did not want to prolong my comment. Also, bone is not a pure metal formation, which is what I think the asker was referring to, but rather a formation that includes "metal" atoms in its composition. Apart from that, your answer is nice and detailed, I just suggest you edit accordingly. $\endgroup$ – Filipe Rocha Apr 10 '17 at 23:56
  • $\begingroup$ @FilipeRocha I am aware of calcium's peculiar properties, but alkaline metals are still, nonetheless, metals. You have, however, reminded me of a certain marine mollusk with iron (goethite) teeth... I also did outline the constituents of bone, so if the OP would like to specify a more restrictive definition of "solid metal," I will be happy to revise. I assume the OP is not referring to truly pure metal, as it would be necessary, obviously, for an organ to sustain cells, so including minerals such as hydroxyapatite in his research would be largely beneficial. $\endgroup$ – CDB Apr 11 '17 at 0:19
  • $\begingroup$ you interested me with those iron teeth! But not every part of the body has to sustain cells - think hair, or a seashell shell (this one I'm not sure!) $\endgroup$ – Filipe Rocha Apr 11 '17 at 0:29
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    $\begingroup$ @FilipeRocha I believe it would be inappropriate here unless the OP asks about them... If not, I will consider asking and answering a question regarding it. I will definitely tag you in it if I do. $\endgroup$ – CDB Apr 11 '17 at 0:37
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    $\begingroup$ @FilipeRocha This is what I love about the stack exchange; everyone has something to add to the conversation :) You are right, we mustn't forget about metal blood! ;) I think the confusion here is coming in because of the loose term of "solid metal." Let us await clarification by the OP. If you think there is more to talk about, I believe we should start a discussion in chat... much more of this and we will effectively bogged down the comments section. :) $\endgroup$ – CDB Apr 11 '17 at 0:43

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