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For my story there exists a fictitious element with special properties. In its pure form is most closely resembles metal (for its physical properties)

This material is quite abundant in salt and oxide forms, but extremely rare in its pure form. There are real life examples of metals hard to get in pure form like Aluminium, due to its reactivity and the strong bonds it makes. However, could there also be a reason a relatively inert metal could bind in ways making it extremely hard to refine, or at least refine to an acceptable purity?

Technology level: Magical technology -> There is a certain balance between the use of magic by people and the application of reality based physical laws, permitting a certain mix of technology and magic allowing for unique technological developments. But for the purposes of metallurgy we can state they're about equally or slightly advanced over our current technological capabilities here on earth.

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    $\begingroup$ Here's a name for your metal: Handwavium. $\endgroup$ – Marvin the Paranoid Android Jan 22 at 13:45
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    $\begingroup$ you go with something with an absurdly high melting point like tungsten which is extracted chemically because reaching its melting point is too expensive and difficult. $\endgroup$ – John Jan 23 at 0:31
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    $\begingroup$ Sounds like titanium to me. Very corrosion-resistant, but very hard to purify. (See the "Production and fabrication" section) $\endgroup$ – ikegami Jan 23 at 4:16
  • $\begingroup$ as ikegami already pointed out. Just google the properties of Titanium and you have your necessary characteristics. (However it is also hard to work with, which might be not what you want). Because titanium is already somewhat abundant and would make a superior metal in a ton of applications. But because its so hard to refine and bring into form its only used where absolutely necessary $\endgroup$ – Hobbamok Jan 23 at 9:26
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    $\begingroup$ do you want a magic tag to go with your question? Because right now it is confusing. the tags reality-check + science-based don't go well with magic. Make your choice. $\endgroup$ – Mindwin Jan 23 at 14:52

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The metal can be either very reactive, as you stated, or it can have a very high melting point, making it unpractical to use smelting based refinement techniques.

Think for example of tungsten which melts at 3422 °C, most crucible and furnace materials will melt or decompose before it does, so how are you going to handle it in its liquid form?

If your fictional metal has an even higher melting point than tungsten, it can satisfy your request.

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    $\begingroup$ Aka your magical metal is basically just Titanium+ $\endgroup$ – Hobbamok Jan 23 at 9:25
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    $\begingroup$ @eagle275 No, tungsten has the highest melting point of any element. Osmium's melting point is "only" 3,033 °C. $\endgroup$ – F1Krazy Jan 23 at 13:20
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    $\begingroup$ If the metal has an high melting point and is also very reactive, aka it can't be reduced in powder for sintering, it will be almost impossible to refine. $\endgroup$ – Stefano Balzarotti Jan 23 at 14:05
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    $\begingroup$ @mindwin, yes I know, but tungsten is not very reactive. I was thinking to a fictitious metal, reactive like Rubidium for example and with melting point of Tungsten. That world be almost impossible to cast. $\endgroup$ – Stefano Balzarotti Jan 23 at 14:32
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    $\begingroup$ @stefanobalzarotti a very reactive metal could be chemically manipulated via its salts and acidic dissolution, creating some precipitates that could be used for alloying. The hard ones to forge would be those in the goldilocks zone between hardness, ductibility, and melting point, probably very stable and non-reactive. That would be a beast to smelt and forge, and probably forget about casting. Casting is not very good for most applications anyway. $\endgroup$ – Mindwin Jan 23 at 14:51
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As an alternative to "hard to refine", I'll propose "dangerous to refine". Your metal is found in more than one natural isotope, where at least one isotope is more or less stable and useful, but the other isotope is radioactive. Isotope separation is quite awkward, even with modern technology, though perhaps magic helps in this regard.

This means that given two separate sources of the metal, one where the safer isotope is more abundant, and one where the unsafe one predominates, the miners, refiners and users of the metal from the hazardous source all end up with cancer and suffer unpleasant injuries, disfigurement and death as a result, whereas the other mine and its products are free from such effects.

Rarity of the metal can therefore be tailored by the relative abundance of the two kinds of site. If the metal was used for magical purposes, handwaving the suitability of one isotope over another for magic would also work.

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    $\begingroup$ "unpleasant injuries, disfigurement and death as a result" haven't stopped any mining activity in the last thousands of years, though $\endgroup$ – L.Dutch - Reinstate Monica Jan 22 at 12:32
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    $\begingroup$ @L.Dutch-ReinstateMonica sure, no-one really cares about the miners, but when the end users get their cool and highly expensive glow-in-the-dark swords and then their hands fall off Pointed Questions Will Be Asked of the vendors. $\endgroup$ – Starfish Prime Jan 22 at 12:44
  • $\begingroup$ Historically, ore deposits should get a lot of notoriety for causing death, and no one would think about making tools out of this metal. But once isotope separation is mastered, they would get useful tools from stable isotopes (like depleted uranium) and really powerful weapons from unstable ones. $\endgroup$ – Alexander Jan 22 at 20:04
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    $\begingroup$ @Alexander or it depends on the decay chain that produces the unstable isotope. $\endgroup$ – Starfish Prime Jan 22 at 20:14
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    $\begingroup$ @ChrisH some science and engineering is amenable to brute force. Fluorine chemistry springs to mind; rocket propellants (especially monopropellants) are another. You read about progress in the obituary column of the newspaper... $\endgroup$ – Starfish Prime Jan 23 at 15:42
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There's a fairly basic contradiction in your posing of the question, which is that the more inert a metal is, the easier it is to purify by definition.

A metal that is abundant as oxides or salts but cannot easily be purified is a metal that is by definition highly reactive; it doesn't want to exist as its pure form because it is so much more stable as a reacted compound. You're not going to get a metal that's "less reactive" but "harder to purify", because these qualities describe opposing things.

The alkali metals, in Groups 1 and 2 of the Periodic Table, fit your definition of "easy to find, hard to purify" pretty well, by being the most reactive metals known to humanity. They react especially quickly to oxygen and to water, both of which are abundant on Earth's surface and are critical to human life, so an environment conducive to human habitation is going to be one that is very poorly suited to the purification of sodium, potassium, rubidium, cesium, lithium, calcium, strontium or barium. The purification of alkali metals typically requires not only high temperature, but water-free and oxygen-free environments (otherwise the metal will just oxidize or hydrolyze again as it cools). The Industrial Revolution was in full swing long before a scalable process for isolating sodium using electrolysis became commercially viable in the late 1800s. Similar work in high-temperature chemistry also gave us a viable method for aluminum refinement, turning what was a precious metal into an important infrastructure commodity in the early 20th Century, and the refinement of silicon, germanium and other "metalloids" that are critical to modern information technology followed in relatively short order in the mid-20th Century.

Alkali metals still aren't commonly seen in pure metallic form, even though sodium is one of the most abundant metals on Earth's surface, because the metals are too reactive for everyday use in their pure form. You can buy the stuff in kilo bricks from chemical suppliers, but about the only household use for it is to make sodium hydroxide for use as a (very strong) cleaning agent, and it's safer all around just to sell that stuff bottled at a useful but not critically hazardous concentration, than to have people dunking sodium metal into water in their mop closets.

The only non-handwaving answer to the question of making a relatively plentiful, inert metal difficult to purify is to require absolute purity. Gold is "24-carat" at 99.95% purity, but that's still one part per 2000 of something else. Last I checked, we've gotten another order of magnitude purer than that (99.995%), but absolutely pure gold has not been achieved on any significant scale. If you need absolutely pure samples of pretty much any substance on earth, you're paying a lot per unit mass, if you can get it at all.

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  • $\begingroup$ Would this mean that the Gold American Eagle coins which aren't pure Gold aren't made from a rare metal & therefore shouldn't be worth so much? Glad I bought 5 nine Canadian Maple Leafs. $\endgroup$ – Rich Bianco Jan 25 at 11:31
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Rare earth elements might be a good example. Good ore sources are rare, they are hard to concentrate, hard to refine and even harder to separate into elemental form as they all tend to occur in the same ore and have very similar chemical properties.

The rare earth elements are reactive metals, but separation difficulty applies to other metals as well such as the Platinum group metals which are also difficult to separate even though they are mostly inert.

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    $\begingroup$ Also don't forget that rare earth elements are often accompanied by radioactive elements like Thorium. This is one of the reasons China is the biggest export nation of rare earth metals: The other countries don't want to bother with the safety aspects. So it is not only difficult, but also dangerous, like Starfish Prime mentioned in his answer. $\endgroup$ – And Jan 23 at 9:09
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Your metal is allotropic, meaning it exists in multiple distinct forms under the same set of conditions (like diamond and graphite). Unfortunately for you, the allotrope that's useful is extremely rare. Refining the material produces 99.99% allotrope A (which is brittle and generally useless) and only 0.01% allotrope B (a metastable state and the form that you're looking for).

There's no known way to directly convert a sample of allotrope A into allotrope B without expending a completely impractical amount of energy. Going the other way is much easier, though. When allotrope B is heated to its melting point at normal ambient pressure, it has a strong tendency to cool into allotrope A form. Metalsmiths have to be extremely careful because traditional metal forging processes risk converting your useful metal into garbage.

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    $\begingroup$ A fun thing with this is if both allotropes are valuable. For instance, we can make carbon nanotubes on the surface of diamond. $\endgroup$ – Émile Jetzer Jan 23 at 10:45
  • $\begingroup$ Does this have anything to do with Gold that I mined personally looks like liquid when I look it it through strong magnifying glass? Was it dangerous for me to mine for that stuff in Idaho? It is some beautiful stuff, almost addicting to hunt for. $\endgroup$ – Rich Bianco Jan 25 at 11:19
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It must be distilled.

This metal has a low melting point and a low boiling point. Heat adequate to smelt it from its salt is adequate to boil it into vapor, which then escapes with the hot gases produced by the forge.

To capture the metal vapor one must use something like a distillation apparatus or fractionation column to capture and condense the hot gaseous metal as it leaves the foundry.

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  • $\begingroup$ Uh, that's not really how distillation works $\endgroup$ – Flydog57 Jan 23 at 18:04
  • $\begingroup$ Or maybe it sublimes directly to a gas and has no liquid phase... $\endgroup$ – Jerry Jeremiah Jan 23 at 20:29
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Titanium is relatively abundant in the form of titanium dioxide, not particularly reactive like the alkali metals, but still quite difficult to refine and even harder to forge. Why? Because even though it's not very reactive under normal conditions, it will still burn, reacting with atmospheric oxygen to turn back into titanium dioxide, at a lower temperature than its melting point.

This means that working with it has to be done with highly specialized furnaces that can hold the metal in an isolated, airtight chamber filled with an atmosphere of non-reactive gases. A society with a strong knowledge of metallurgy would still struggle with this unless they also have a similarly advanced understanding of chemistry and atomic theory.

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    $\begingroup$ Elsewhere, Titanium was known as Mithril .... $\endgroup$ – nigel222 Jan 23 at 16:58
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    $\begingroup$ Titanium cannot be refined in a pure nitrogen atmosphere, as Titanium Nitride is formed well below melting temperatures. Halogen environments are required. $\endgroup$ – Tangurena Jan 23 at 17:23
  • $\begingroup$ @nigel222 Oh, have you been reading Paul Twister? $\endgroup$ – Mason Wheeler Jan 23 at 19:23
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It's not difficult to refine; magic makes the process unpredictable

Several other answer mention the dichotomy between being inert and being difficult to refine. So, turns out it IS really easy to refine, it's just that part of it's inert nature is absorption of magic. When the metal is refined, the magic is released in a very uncontrolled manner. So the difficulty isn't the actual process of refining it, it's in putting up wards in a way that keeps the blacksmith from becoming a frog, or the crucible turning to jello or any other wild effect caused by a sudden concentration and disbursement of undirected magic.

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  • $\begingroup$ That's awesome! $\endgroup$ – Jerry Jeremiah Jan 23 at 20:33
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Rare earths already being suggested, I suggest something similar - Zirconiunm + Hafnium.

They are very similar in chemical properties, found together in nature and rather hard to separate, zirconium is used in nuclear technology for being transparent to neutrons, hafnium is a neutron poison. If you need zirconium in a nuclear reactor, you need zirconium at insane purity level in regard to hafnium. If you need it for something else, an natural alloy of both metals is just OK.

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Hydrogen

Just remembered, that deep inside Jupiter Hydrogen is a metal. Some think it would be metastable at room temperature and pressure, if only we could make some.

You would need some serious thaumaturgy to convert the gas into a metal, and perhaps a touch of persistent magic to prevent it from converting back.

Now, what use would it be to your plot?

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Magical Chemistry

The reason this element is very hard to define is that it has an affinity for a certain type of chemical bond which has magical properties.

As a result, this element is only ever found in nature when it is bound up in this type of molecule (ore).

This chemical bond can, therefore, only be disrupted either by direct manual application of magic in the proper form (not scalable) or by using a catalyst with the right magical properties itself (very expensive in time, money, and resources). For added drama, this catalyst could be explosive, corrosive, poisonous, and/or radioactive.

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Perhaps the difficulty could lie not just in the properties of the metal (as others have stated, an extremely high melting point is a great answer based on physical properties of the metal) but in the distribution of the element on your world and its bonding with other elements.

Example One: A metal—let's call it Unrefinium—is very abundant towards the core of the planet. A volcanic eruption, or series of eruptions over the history of the planet sent particulate sized debris of this metal across the planet. It is highly abundant in a difficult to reach location, but all of its concentration towards the surface of the planet is distributed like grains throughout the world, maybe 50ppm in an average soil sample.

Example Two: The metal has a very low boiling point. In one of its forms, the metal is extremely reactive with another element present in the water supply of the planet. While abundant, it is generally bound and traveling through the water cycle. It evaporates and precipitates every time it rains and is present in any body of water, but must first be isolated, then refined.

In both these examples, the difficulty of refining it comes from the sheer amount of substrate material required to obtain it, and the energy necessary to remove it from other compounds. Being extremely reactive, you could have a high binding energy with other compounds be a limiting factor as well.

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Caesium

Just because nobody has yet mentioned it. It's not exactly common, but that's not the main difficulty. It is incredibly reactive -- explosive, even -- in contact with air, water, and careless alchemists. In a low-technology environment, magic would be the only way to extract it. (Youtube has videos of small amounts of Caesium being introduced to water. Worth watching! )

The same goes for Titanium, but somebody else has already covered it. the only reason it doesn't go kaboom much like Caesium, is that the oxide layer that forms over the metal protects it from further reaction.

Also Rubidium, the same to a lesser degree. Even Potassium would be difficult. Just as Copper, Silver, Gold for scarcity and nobility (non-reactivity), so Potassium, Rubidium and Caesium for scarcity and increasing reactivity.

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Your metal isn't rare, but it's not concentrated anywhere and is therefore hard to mine and refine economically. A real life example of this is scandium, which is more common in the Earth's crust than tin or lead, but, owing to its chemical properties and geochemical processes, it's spread out everywhere and there are few places where it can be economically mined. Only about 15 tons are mined per year!

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  • $\begingroup$ Because IIRC the only use for Scandium is as small percentages to toughen up alloys used in aerospace. The cost of Scandium limits their use, but if new uses were to arise for these expensive alloys, more Scandium would be mined. $\endgroup$ – nigel222 Jan 23 at 16:56
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You have posed a dilemma: you prefer a material that is inert, but inert materials aren't going to do the salts and oxides thing at all; anything inert prefers to stay out of compounds of any kind.

Instead, you might want to put the special properties to an isotope of a common element; the useless isotope being abundant, and the useful one the rare exception mixed in.

This lets you set up things so that you can easily acquire loads and loads of the useful isotope, but it's prohibitively expensive to separate the good stuff from the useless garbage it's diluted with: the isotopes are going to have similar boiling and melting points, and they are very much like each other by all chemical properties too. (You can still drink heavy water, even though it's a bad idea to do so)

Real world example: It's notoriously difficult to enrich the particular isotope of uranium suitable for the most preferable nuclear reactors: you need a large building's worth of high-speed, high-precision centrifuges to separate the good stuff from the chaff.

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  • $\begingroup$ Didn’t see this before I posted a similar answer. $\endgroup$ – WGroleau Jan 22 at 23:33
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It is fairly inert, but in ores, it is normally in very small grains mixed with equal amounts of another inert mineral. The reason they are hard to separate is that they are very similar in melting point and specific gravity..

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This question reminds me of Naq-Alrama steel as used in the wandering inn

It's a tricky metal, but highly sought after, that can only be refined under moonlight, weaving the moonlight into the metal, as soon as sunlight touches the ingots, they are ruined, It's only stable after final forging. Even the proper forging happens in airless conditions with extreme heat, and it takes years to master the skill of refining and shaping the metal, and it's a closely guarded secret.

Since you're having a magical technology world, you could imbue such a thing too. Special radiation, life essences, nature harmonics needed to occur to be able to break the bonds that make it oxidize and react with impurities and secure the pure form. This does mean it will be susceptible to any disturbances, just like 100% pure water will try to dissolve and absorb the molecules of the container it is held in.

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Smelting often requires catalysts to be added to the molten metal to bind with it (or the impurities) to help separate the good stuff from the bad. Perhaps your metal requires rare, dangerous, or unstable catalysts?

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Instead of making the metal chemically rare in a certain form, why not make it historically rare? Eg

  • the metal is naturally consumed by a bacteria which ionizes or deionizes it, hence because this bacteria is common it is hard to find the inert form of the metal.
  • some historical event stripped the world of most of the inert metal, eg, the rarity of the metal used in the armor in the Mandalorean series.
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Some classic examples are niobium/tantalum and zirconium/hafnium. These elements are extremely difficult to separate, and indeed hafnium was one of the last stable elements to be discovered. If it has desirable properties for your scenario, you can't do much better.

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