Zeolite formation

I read in a book that zeolites are formed by Aluminium replacing a silicon atom in Silicon dioxide. It says there is a negative charge formation. How does this happen? Thanks.




There's no magic in this - just the beauty of science.


* Imagine a lattice of $\ce{Si^{(+4)}O4}$ tetrahedrons ($\ce{Si}$ in the centres, $\ce{O}$ on the corners) connected through the edges corners (= the $\ce{O}$ atoms)
* Replace some of the $\ce{Si^{(+4)}}$ with $\ce{Al^{(+3)}}$


As a result, the whole lattice becomes a huge polyanion. 


The charges are balanced via cations, such as $\ce{H+}$, $\ce{Na+}$, etc. embedded in the pores of the lattice. 


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