natrolitegroup

The natrolite group is a subdivision of the zeolite family of minerals defined by the natrolite-type aluminosilicate framework. Members are hydrated aluminosilicates formed by linking AlO4 and SiO4 tetrahedra to create a porous three-dimensional structure that hosts water molecules and exchangeable cations in its channels. The idealized formula for natrolite is Na2Al2Si3O10·2H2O, but members vary in dominant cations such as sodium, calcium, or others, producing different chemical compositions within the group.

Structure and properties: The minerals crystallize in monoclinic or other crystal systems depending on the member, and crystals are typically acicular or prismatic, often colorless to white. They are relatively soft, with a Mohs hardness around 5 to 5.5, and are known for their characteristic porous frameworks that accommodate water and cations.

Occurrence and formation: Natrolite-group minerals form as secondary alteration products in volcanic rocks such as basalts and rhyolites, as well as in hydrothermally altered rocks. They commonly occur in cavities and veins and are frequently found together with other zeolites and secondary minerals, reflecting low-temperature crystallization conditions.

Distribution and significance: They are widely distributed in zeolite deposits worldwide and are of interest for petrographic study and crystal-chemical research. While not major ore minerals, natrolite-group minerals contribute to understanding low-temperature diagenetic and hydrothermal processes and the broader chemistry of zeolite minerals.