Iron ore

Iron ore is naturally occurring material from which iron can be extracted under the relevant technical and economic conditions. Important iron-bearing minerals include hematite, $\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$, and magnetite, $\mathrm{F}{\mathrm{e}}_3{\mathrm{O}}_4$. Real ore also contains other minerals, so its composition differs from that of a pure iron oxide.^[ref]

Using approximate atomic masses, pure hematite contains $2(55.85)/(2(55.85)+3(16.00))\approx 69.9\%$ iron by mass. This is a mineral-composition calculation, not the grade of every ore deposit. Beneficiation, transport and removal of oxygen and unwanted constituents all influence whether a deposit is a useful feed for iron extraction.