Description
Zeolites are minerals belonging to the tectosilicate family. Natural zeolites can contain a lot of water. When heated, this water boils out, hence the name "zeolite," from the Greek "zein," meaning "to boil," and "lithos," meaning "stone." There are approximately fifty natural zeolites and more than a hundred artificial zeolites. Common natural zeolites include natrolite, heulandite, and stilbite. Artificial zeolites are used in detergents, cat litter, and catalysis, among other things. A zeolite is composed of silicon, aluminum, and oxygen atoms. These atoms form tetrahedra, which in turn can form cages. This gives the zeolite a highly porous structure. However, the structure of a zeolite is very regular, and the interconnected cages form a kind of channel. These channels can be imagined as corridors and elevator shafts in an apartment building. The cages can contain small molecules (such as water) and ions. The ions are often needed to compensate for the negatively charged structure of Si, Al, and O. Heating the zeolite at high temperatures can cause the structure to collapse. Further heating of this amorphous material can nucleate a new ceramic phase. The following zeolites are known: Analcime – NaAl(Si2O6)·(H2O) Clinoptilolite – (Na,K,Ca)2-3Al3(Al,Si)2Si13O36·12(H2O) Laumontite – CaAl2Si4O12·4(H2O) Chabazite – (Ca0,5,Na,K)4[Al4Si8O24]·12H2O Gismondien – Ca2Al4Si4O16·9(H2O) Mazzite – 2CaMg2(Al,Si)36O72·28(H2O) Heulandite – (Ba,Sr,K,Ca,Na)2-3Al3(Al,Si)2Si13O36·12(H2O) Stilbite – NaCa4Al8Si28O72·30(H2O) Natrolite – a2Al2Si3O10·2(H2O) Mordenite – (Ca,Na2,K2)Al2Si10O24·7(H2O) Gottardiite – a3Mg3Ca5Al19Si117O272·93(H2O) Brewsterite – (Sr,Ba)Al4Si12O32·10(H2O)
