Composition of Portland Cement before Hydration
According to Ullmann’s Encyclopedia of Industrial Chemistry (sixth edition), Portland cement consists mainly of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and calcium aluminoferrite.

$$
\textbf{Phase composition of Portland cement clinker} \\
\begin{array}{llll}
\hline
\text{Constituent} &amp; \text{Formula} &amp; \text{Content in wt %} \\
&amp; &amp; \text{Range} &amp; \text{Average}\\
\hline
\text{Tricalcium silicate} &amp; \ce{3CaO.SiO2} &amp; 46{-}79 &amp; 61 \\
\text{Dicalcium silicate} &amp; \ce{2CaO.SiO2} &amp; 5{-}30 &amp; 15 \\
\text{Calcium aluminoferrite} &amp; \ce{2CaO.(Al2O3,Fe2O3)} &amp; 4{-}16 &amp; \phantom{0}8 \\
\text{Tricalcium aluminate} &amp; \ce{3CaO.Al2O3} &amp; 6{-}18 &amp; 12 \\
\text{Free calcium oxide} &amp; \ce{CaO} &amp; 0.1{-}4 \\
\text{Free magnesium oxide} &amp; \ce{MgO} &amp; 0.7{-}1.5 &amp; \phantom{0}1.5 \\
\hline
\end{array}$$

Büchel, Moretto, Woditsch Industrial Inorganic Chemistry (second edition) lists the same six constituents as important clinker phases. This reference also includes a diagram for the three component system $\ce{CaO}$–$\ce{SiO2}$–$\ce{Al2O3}$ with composition ranges for various cement types, which shows that calcium monosilicate (CS) is not necessarily within the typical range for Portland cement.



Furthermore, this reference includes a table with a typical chemical analysis of a Portland cement, which shows that the $\ce{CaO}$–$\ce{SiO2}$ ratio is too high for calcium monosilicate and also indicates that small amounts of phosphate could be present:

$$
\textbf{Typical chemical composition of a Portland cement clinker} \\
\begin{array}{ll}
\hline
\ce{CaO} &amp; 58{-}67\ \% \\
\ce{SiO2} &amp; 16{-}26\ \% \\
\ce{Al2O3} &amp; \phantom{0}4{-}8\ \% \\
\ce{Fe2O3} &amp; \phantom{0}2{-}5\ \% \\
\ce{MgO} &amp; \phantom{0}1{-}5\ \% \\
\ce{SO3} &amp; \phantom{0}0.1{-}2.5\ \% \\
\ce{Mn2O3} &amp; \phantom{0}0{-}3\ \% \\
\ce{P2O5} &amp; \phantom{0}0{-}1.5\ \% \\
\ce{TiO2} &amp; \phantom{0}0{-}0.5\ \% \\
\hline
\end{array}$$