Zeolites belong to a large family of minerals that includes nearly 200 types. Natural zeolites form a small group of about thirty species in this large family. Natural zeolites were formed by the transformation of volcanic ash that was deposited in lakes and seas tens of millions of years ago. Natural zeolites are aluminosilicate of hydrated alkali or alkaline earth metals.

These non-toxic minerals are often called “molecular sieves” because of their porous and open structure formed of cages connected by a vast network of interconnected channels that can be roughly compared to a “honeycomb”. Positively charged atoms (cations) such as alkali or alkaline earth metals are linked with negatively charged aluminosilicate lattice structure. These cations can be replaced by others having a greater affinity for the inorganic matrix, which gives zeolites one of their main characteristics: the cation exchange capacity.

The channels have a size close to that of a molecule of water so that the smallest molecules can penetrate the zeolite’s pores while the largest ones cannot pass through, thus giving rise to the term “molecular sieve”. Zeolites generally have high specific surface areas: Their rigid structure gives them great stability because they do not swell. However, the mineralogical composition, surface area, density and cation exchange capacity (CEC) of each zeolite determine its overall properties and therefore its effectiveness for a given-application.