Oxidation states of the metal in the minerals haematite and magnetite, respectively, are:

Hematite is an ore containing oxide of iron with the molecular formula  ${\mathrm{Fe}}_2{\mathrm{O}}_3$                  

For ${\mathrm{Fe}}_2{\mathrm{O}}_3$​, let the oxidation number assumed to be X
So, 

$$\begin{gathered} 2\mathrm{X}+3(-2)=0 \\ \Rightarrow \mathrm{X}=+3 \end{gathered}$$

$\stackrel{+3}{{\mathrm{Fe}}_2{\mathrm{O}}_3}$ (Haematite),

Magnetite is one of the main iron ores found in the earth's crust. A chemical formula is ${\mathrm{Fe}}_3{\mathrm{O}}_4$.  It is the stoichiometric composition of FeO and ${\mathrm{Fe}}_2{\mathrm{O}}_3$ .
For, $\mathrm{FeO}$, let the oxidation number assumed to be X
So,

 $$\begin{gathered} \mathrm{X}+(-2)=0 \\ \Rightarrow \mathrm{X}=+2 \end{gathered}$$

For, ${\mathrm{Fe}}_2{\mathrm{O}}_3$​, let the oxidation number assumed to be X

So, $$\begin{gathered} 2\mathrm{X}+3(-2)=0 \\ \Rightarrow \mathrm{X}=+3 \end{gathered}$$

${\mathrm{Fe}}_3{\mathrm{O}}_4\Rightarrow \stackrel{+2}{\mathrm{F}}\mathrm{eO}\cdot {\stackrel{+3}{\mathrm{F}}\mathrm{e}}_2{\mathrm{O}}_3$ (magnetite)