Black 2013 UK 10p coin

Hi, I just thought post some pictures of an unusual-looking 10p coin from 2013. It's black!!!
Was just wondering if anyone here has seen anything like it before, owns something similar or has any information because I've look a lot on line for info but have been able to find anything about a coin like this.

It has been in a fire, probably.
The black is not from the coin itself, but ash from whatever it was next to, probably wood.
If it was made of copper and not copper-nickel it would look like
this 1787 token I have, which has been burnt in the past ...

Then again it could have been darkened by chemicals, for some reason.
I know sodium thiosulphate was used to darken newly-minted copper coins
over 100 years ago so they could not be confused with gold coins. UK 1/4d for example.
Not sure what would darken copper-nickel.

After being buried in soil, copper-nickel turns black.