Formula: KCa4Si8O20F.8H2O
Phyllosilicate (sheet silicate), apophyllite group, forms a series with hydroxyapophyllite-(K)
Specific gravity: 2.33 to 2.37
Hardness: 4½ to 5
Streak: White
Colour: Colourless, pale green, aquamarine, white, pink, yellow
Common impurities: Al,Na

Igneous environments
Metamorphic environments
Hydrothermal environments
Basaltic cavities

Historically all the apophyllite group minerals were reported simply as "apophyllite", and indeed it requires analysis to differentiate between them, so there is comparatively little information about the individual members of the group, except in recent times. See the apophyllite page for more information.
Fluorapophyllite-(K) is a secondary mineral in cavities in basalt, cavities in granite, in tactites and in some hydrothermal veins (Mindat).


At the Basalt Quarry, Ambariomiambana, Ambohimalaza Commune, Sambava District, Sava, Madagascar, fluorapophyllite-(K) crystals to 3 cm have been found in small cavities in the main quarry wall (Min Rec 41-3.242).

At the Wiwatersrand goldfield, South Africa, fluorapophyllite-(K) is found rarely, and always with quartz, which it postdates. Specimens have been recovered from the Stilfontein and Mponeng mines, coloured colourless through white to pale green, the last caused by secondary mineral inclusions (R&M 96.4.324-325).

At the Dara-i-Pioz Glacier, Districts of Republican Subordination, Tajikistan, Fluorapophyllite-(K) is an associate of fluorapophyllite-(Cs) (CM 57.965–971).

At Fanwood Quarry, Watchung, Somerset county, New Jersey, USA, only a handful of specimens of fluorapophyllite-(K) are known to exist. Glassy crystals up to 1 cm on datolite have been collected in the middle amygdaloid (Minrec 41-2.166).

At the Braen Quarry, Haledon, Passaic county, New Jersey, USA, fluorapophyllite-(K) is relatively uncommon and occurs as isolated crystals on datolite, prehnite or calcite or directly attached to the walls of breccia cavities (Min Rec 40-6.516).

At Wind Mountain, Cornudas Mountains, Otero county, New Mexico, USA, fluorapophyllite-(K) is an associate of windmountainite (CM 58.477-509).

At New York City, New York, USA, lustrous white fluorapophyllite-(K) crystals are found filling seams in schist and gneiss. Beneath Roosevelt Island, plates to 21 cm across of colourless, transparent to translucent fluorapophyllite-(K) crystals to 12 mm have been. Tabular, translucent, greenish fluorapophyllite-(K) crystals to 18 mm across have been recovered from the tunnel in areas under Queens and Manhattan (R&M 84.3.226).

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