In that case you get to investigate it yourself as to what might go.
There are various schools of thought there.https://mana.fandom.com/wiki/Sword_of_Mana_(weapon
Fan thing on the sword of mana as it appears in various games. What games you want to include in the canon would have to be figured out there as there are a few and we are now quite far from what the original creators might have been envisioning.
While I said about rust before then I would suppose I get to consider that a) many people say rust or rusted and just mean metal oxides rather than oxides of iron which would be the more chemical/metallurgical definitions and b) that the article there mentions magic which changes the whole process massively ( https://www.youtube.com/watch?v=0zBsUdUKmhk
for but one exploration of things there).
Where did "Gundanuim" come in here? Also I presume that was a typo and was instead supposed to be "Gundanium" for other than Americans and "aluminum" then most elements, metals and alloys thereof that go in for the a suffix like that will end with ium (see also the periodic table).
Either way of spelling I have never heard of it or anything like it (gun metal being about the closest, though there is of course the term in the gundam series which is a different matter entirely; a search there says it is very much a technical feat in that franchise where this is high magic fantasy) so would presume it is something invented for the series, or maybe more mythological. That said mithril is a myth so it might be something there (though I would like to believe I have a reasonable grasp of the myth of most places here), and despite being a metallurgist then 99% of what I will know is anything used industrially and 95% of that for most will be steel and its alloys so could well have sailed by me.
If it is mentioned in the game (would have thought the wiki article above would note it but oh well) then a) is it a thing made up for the translation, b) from a reliable narrator within the game and c) a term within the game lore that might mean something else today (star metal today would be called meteoric iron for iron/steel is really quite difficult to make and prior to various processes being discovered that would be the main source of it, also the stuff typically found in it makes it nothing like modern steels or even human made steels from medieval periods onwards).