What is (if there is) the reaction between manganese chloride and oxygen when dry?

I had a chemistry lab and I did a error. I was supposed to make some $$\ce{MnCl2}$$ and then used fire to dry it but then some of it turned black, and I am supposed to quantify my error. So I am assuming the reaction to be between $$\ce{MnCl2}$$ and $$\ce{O2}$$ but I don't know what they make.

Heating $$\ce{MnCl2}$$ in presence of air made it to oxidize and form black manganese oxides.
$$\ce{4MnCl2 + 3O2 ->[\Delta] 2Mn2O3 + 4Cl2}$$