\begin{table}%T1
\caption{Elemental oxide compositions of three types of precursor
material in weight percentages and the calculated liquidus
temperatures. The compositions are the same as listed
\citep{yu1998} except that the small amounts of K$_2$O
($<$0.11\%) were not included and magnetite (Fe$_3$O$_4$) was
used in place of FeO.} \label{tab:comp}
%\centering
\par
\begin{tabular}{lccc} \hline\hline
            & \underline{Type~IA}& \underline{Type~IAB} &
\underline{Type~II} \\
SiO$_2$         &   45.4   & 47.2  &  49.2  \\
TiO$_2$         &   0.1    & 0.1   &  0.1   \\
Al$_2$O$_3$     &   4.9    & 9.7   &  4.1   \\
Fe$_3$O$_4$     &   8.3    & 6.6   &  21.3  \\
MnO             &   0.1    & 0.1   &  0.1   \\
MgO             &   37.4   & 30.7  &  22.7  \\
CaO             &   2.5    & 3.5   &  0.2   \\
Na$_2$O         &   1.3    & 2.1   &  2.3
\\[2pt]
Liquidus   \\
~~temperature     & 1692~\degr C     &1577~\degr C
&
\up{1509~\degr C}\\
\hline
\end{tabular}\normalsize
\end{table}