= 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>, $\mathrm{Fe_2O_3}$, and <magnetite>, $\mathrm{Fe_3O_4}$. Real ore also contains other minerals, so its composition differs from that of a pure iron oxide.<Iron Ore by South Australia Energy and Mining>[South Australian government, iron-ore minerals and uses]{ref}
Using approximate atomic masses, pure <hematite> contains $2(55.85)/(2(55.85)+3(16.00))\approx69.9\%$ <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>.
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