Zeolites are tectosilicates consisting of interlocking SiO4 and AlO4 tetrahedrons, which share oxygen atoms. Whilst the SiO4 groups are neutral, AlO4 carries a negative charge, which has to be balanced by positively charged ions. Because the structures are very open, these can be quite large, allowing space for large metals such potassium and calcium and even strontium and caesium. Another effect of the openness is to allow these ions to move around.

The name Zeolite was originally used by Axel Cronstedt who observed, when rapidly heating a specimen, that the crystals began to move around as the water boiled off. Using the Greek words which mean "stone that boils," he called this material Zeolite. The presence of water was a major discovery, and significantly, its removal was found not to damage the crystal structure. In fact the loss was reversible, water being rapidly reabsorbed on immersion in the liquid.

Zeolites typically form in the cavities of volcanic rocks, and are the result of low grade metamorphism. They generally form as a result of the reaction between igneous, silica-poor rocks, and water. The reaction temperature range is from 27°C to 55°C and nature requires 50 to 50,000 years to complete the reaction. The number of naturally occurring Zeolites is large with over 60 recognised species. However, about half of these have only ever been found as tiny microcrystals and most are rare.

Zeolites have basically three different structural variations. There are chain-like structures whose minerals usually form needle-like crystals, as found in Natrolite. There are sheet-like structures where the crystals are tabular as found in Heulandite. Lastly there are also framework structures where the crystals are more isometric, as found in Chabazite. These variations give the Zeolite group, many pleasing crystal forms.

As a group they are common and widespread around the world. Famous localities include Scotland and Iceland. Until eclipsed by the discovery of Zeolites in the enormous Daccan basalts of India in the early 20th century, the Bay of Fundy was world famous for its specimens. It still produces world-class examples.