Apophyllite

Apophyllite, Heulandite, Stilbite
Apophyllite on Stilbite

"Apophyllite" refers to a group of three minerals that exhibit similar chemical properties. The three species of apophyllite are Fluorapophyllite-(K), Hydroxyapophyllite-(K), Fluorapophyllite-(Na). Apophyllite minerals containing more Fluorine in relation to other species are classified as Fluorapophyllite, while Apophyllite minerals containing more hydroxide in relation to other species are classified as Hydroxapophyllite. Apophyllite occurs in a variety of colors, including green, clear, purple, and yellow. 

Uses

Apophyllite is valued among mineral collectors. Other Zeolites related to Apophyllite, enabled by their molecular structure allowing water to bypass crystals, are used for numerous water-related filters.

Notable Localities

Apophyllite occurs in basalt traps throughout the world, most notably in the Maharashtra province in India.

Properties
Chemical Formula(K,Na)Ca4Si8O20(F,OH)·8H2O
Hardness4.5-5
Crystal SystemTetragonal
Mineral ClassSilicates
LusterVitreous, Pearly