Inconsistent aluminium descriptions

Hello everyone, today I thought I'd look through all the aluminium coins in my collection using numista, when I noticed that a good number of them were missing. As it turns out, many 95%+ aluminium coins (for instance from Austria or Ruanda-Urundi) are not listed as aluminium coins, but as aluminium-magnesium coins. I understand there may be a very slight difference with pure aluminium coins, but then I saw with the 3 aluminium Ruanda-Urundi coins that every single one of them was listed differently.

The 50c piece just says aluminium, the 1fr piece says aluminium with the more detailed composition between brackets, and the 5fr piece says aluminium-magnesium with the same bracket composition as the 1fr. Which one of these is listed correctly? And is the 10 groschen the only non-aluminium-magnesium aluminium coin from Austria?

I highly doubt there are any pure aluminum legal tender circulating coins anywhere. They would be much too soft to last more than a couple of months in circulation. The 10 groschen coin listed as aluminum is almost certainly the same aluminum magnesium alloy as the 2 groschen coin.  Pure aluminum on a magnetic slide travels down even slower than 900 silver and both of the two Austrian aluminum coins slide down at the same rate (slower than pure aluminum).

I'd tend to agree with rsirian1 but finding information on the level of magnesium isn't easy. One of the few examples I thought I knew was this 50 centimos. I have it in a mint set and the composition is given as 96.5% aluminium, 3.5% magnesium. However, we have “Aluminium (96% aluminium, 3.5% magnesium, 0.5% manganese)”. Has that come from the Madrid mint? Digging into the UK Royal Mint reports, they started assaying aluminium coins in the 1960s and report magnesium contents of around 3.5%. However, there's no mention of any alloying for the earlier pieces struck for East and West Africa.

There are cases of pure auminium coins being issued for circulation. For example, the US Mint and the Nepali Central Bank reported that these coins are made from pure aluminium.

Additionally, the Japanese 1 Yen and South Korean 1 Won are also pure aluminium.

Yes, I have some coins listed as 100% aluminum.  I tested them on my magnetic slide against a pure aluminum disk (99.9999% aluminum, scientific research grade) and they slide down faster then the pure aluminum but significantly slower than a coin listed as aluminium-magnesium.  So yes, 100% aluminum as in "commercially pure" but enough other element(s) to increase their abrasion/wear resistance some.

There is scientific need for distinction, however, I believe that search could be ammended to show both Aluminium and Aluminium-magnesium when searching for any one of them, as these are undistinguishable without scientific instruments.

So are we going to have to change the description to just aluminium with the special composition between brackets or is this change you propose going to be implemented?

Multi selection of search terms would be a solution like where you check boxes. Otherwise we would need a family terms like Aluminium and alloys, Copper and alloys … ad infinitum.

Do XRF machines have the ability to correctly identify the amount of aluminum and magnesium in coins?

I know they are normally used for silver and gold, but has anyone tried them on aluminum?

XRF is not very good for light elements like aluminium as well as lithium, beryllium, sodium, magnesium, silicon and phosphorus.