Provide information on the percentage proportion of elements and mixtures present in Portland cement.

(N/A) The average composition of Portland cement is:
$CaO: 50-60 \%, SiO_{2}: 20-25 \%,$
$Al_{2}O_{3}: 5-10 \%, MgO: 2-3 \%,$
$Fe_{2}O_{3}: 1-2 \%, SO_{3}: 1-2 \%$
For a good quality cement,the ratio of silica $(SiO_{2})$ to alumina $(Al_{2}O_{3})$ should be between $2.5$ and $4$,and the ratio of lime $(CaO)$ to the total of the oxides of silicon $(SiO_{2})$,aluminium $(Al_{2}O_{3})$,and iron $(Fe_{2}O_{3})$ should be as close as possible to $2$.