Australia 50 cents

Hi everybody!
I have got this coin in my collection:
https://en.numista.com/catalogue/pieces6178.html
And than I find another coin like that but gold. I searched everywhere and I could not find anything. Here are the pictures:


It's weight is 15,86 g and weight of normal coin is 15,55. Diameter is normal. Please, help me identify that coin and tell me the value of that coin.
Thank You!
Kuna

Possibly gold plated. It would explain the marginal weight difference.  

Απόσπασμα: bam777Possibly gold plated. It would explain the marginal weight difference.

Well, maybe. But why would someone do that? Is that means that it is unique?
What is it worth?
Thank You!

Unique?  Maybe.  Value?  I'd say a solid 50 cents.

Απόσπασμα: glorkarUnique?  Maybe.  Value?  I'd say a solid 50 cents.

Well, at least I can buy myself a cup of coffee.  
ooohhhh!
Should I add that coin in tokens or not?

Nah.  Just mark it as a normal one, but if you want to, you can put a comment for your own records that it's plated.

OOOOHHHH!
OK!
Thank You!
But I also have a normal one.  

I would give it to a kid you know, hopefully it'll spark an interest plus he/she will have this amazing gold coin like nobody else has !

Hi I thought I would re-visit this thread, as I was at a coin fair last weekend and came across someone selling the Cook coins, still in the original commemorative cases and they all had this toning, either full or some part of the coin. It must have been a reaction to the plastic in which the case was made from.

If you search on eBay you can also see a fair few of them have it. Not all, as 550,000 were sold in cases, 16,000,000 were released into circulation.

But how can You explain the differences in weight if it is normal coin but from the case.
Regards

Απόσπασμα: KunaBut how can You explain the differences in weight if it is normal coin but from the case.
Regards

That I cannot explain sorry