Apophyllite-(KF) or fluorapophyllite is a
mineral of the
apophyllite group, with the chemical formula of KCa
4Si
8O
20(F,OH)ยท8(H
2O). It gets the first half of its name, "fluor", from containing more
fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
than
hydroxide compared to the other minerals in the apophyllite group.
Fluorapophyllite crystallizes in the
tetragonal crystal system. Tetragonal minerals have three axes of different lengths and angles of 90 degrees. Fluorapophyllite is an anisotropic mineral and has low relief. This mineral belongs to the uniaxial (+) optical class, which means its indicatrix has a prolate sphenoid shape with a circular section, principal section, and one optic axis.
Among the apophyllite group, fluorapophyllite is the most abundant compared to the other two minerals in the group, hydroxyapophyllite and natroapophyllite. It is popular among many mineral collectors because of the large, well-developed crystals they form and the multiple colors they come in. The most wanted variation of fluorapophyllite is the green colored variant, which is found in India. Fluorapophyllite is also found in New Jersey of the United States.
[Cook, Robert B. (1995) Fluorapophyllite. Rocks and Minerals, 70. 394-398.] This mineral is found as a secondary mineral in
vesicles in
volcanic rocks such as
basalt.
Images
File:Fluorapophyllite-Stilbite-Ca-indi-94b.jpg, Stilbite crystals surround a pastel green, translucent fluorapophyllite crystal
File:Apophyllite-(KF)-66684.jpg, Isolated apophyllite cluster on contrasting matrix
File:Apophyllite-(KF)-131740.jpg, A radial cluster of cubically-tipped apophyllite crystals
File:Apophyllite-(KF)-Stilbite-Ca-Calcite-171681.jpg, Light green form from Pune District, Maharashtra, India
References
{{commonscat, Fluorapophyllite-(K)
Phyllosilicates
Tetragonal minerals
Minerals in space group 128