\begin{table}%t1
\caption{\label{t:chem}Overview of our sample minerals, their origins and chemical
compositions. }
\small%\centering
\par
\begin{tabular}{llll}
\hline\hline
Mineral name & Ideal sum formula & Actual sample composition & Sample origin\\
\hline
picrolite       & Mg$_6$[Si$_4$O$_{10}|$(OH)$_{8}$]  
                  & Mg$_{5.84}$Fe$_{0.17}$[Si$_4$O$_{10}|$(OH)$_{8}$] 
                  & Black Lake Mine, Canada \\
talc            & Mg$_3$[Si$_4$O$_{10}|$(OH)$_{2}$]    
                  & Mg$_{3.33}$Fe$_{0.1}$[Si$_4$O$_{10}|$(OH)$_{2}$]
                  & Murcia, Spain \\
chamosite       & (Fe,Al)$_6$[(Si$_3$Al)O$_{10}|$(OH)$_{8}$] 
                  & Fe$_{3.55}$Al$_{1.88}$[Si$_3$AlO$_{10}|$(OH)$_{8}$] 
                  & St.Brigitte, France \\
montmorillonite & (Mg,Al)$_2$[Si$_4$O$_{10}|$(OH)$_{2}$] & Al$_{1.5}$Mg$_{0.25}$Fe$_{0.18}$[Si$_4$O$_{10}|$(OH)$_{2}$] & Wyoming (USA) \\
& (Na,K,Ca)$_x$~.~nH$_2$O  &  (Na,K)$_{0.06}$~.~1.2H$_2$O & \\
\hline
\end{tabular} 
\end{table}