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Apophyllite is a frequent associate of zeolites, but it is not a zeolite itself. It is a so-called phyllosilicate - a 'leaf silicate' - where zeolites are 'framework silicates'. It may seem odd to start off saying, what Apophyllite is not, but a number of dealers and collectors believe it is a zeolite because of it's mode of occurrence - blocky crystals in vesicles of basalt with zeolites.
Though by far most specimens in collections come from basalts, particularly from the Deccan Plateau in India, Apophyllite is known from other kinds of deposits, and indeed the type locality - Utš in Sweden - is a Magnetite deposit in gneiss. Pink crystals of Apophyllite occur as a rare associate mineral in the silver mines of St. Andreasberg (Harz, Germany), and the mineral is also known from the alkaline pegmatites in Langesundsfjord (Norway) and Andradite skarn in Långban (Sweden).
Apophyllite crystals are tetragonal, and have a square cross-section, and the very distinct cleavage planes have a strong pearly luster. Apophyllite is a mixture of two hypothetical end-members, Fluorapophyllite and Hydroxylapophyllite, where fluorine and hydroxide may substitute for each other. Which dominates, depends on the locality, but most Apophyllite specimens are Fluorapophyllite, however, we will only designate specimens as specifically 'Fluorapophyllite' or 'Hydroxylapophyllite' if we have a good reason to assume one or the other dominates. The two end-members are freely miscible, can not be distinguished visually, and it is hardly worthwhile analysing each individual specimen. Apophyllite is not used industrially.
My records indicate that Apophyllite from a range of deposits occurs on specimens that also carry one or more of the following minerals: Analcime, Babingtonite, Barite, Calcite, Celadonite, Chabazite, Chrysocolla, Datolite, Dioptase, Epidote, Ettringite, Fluorite, Galena, Gilalite, Gmelinite, Goethite, Grossular, Gyrolite, Harmotome, Heulandite, Illite, Inesite, Kinoite, Laumontite var. Leonhardite, Mesolite, Natrolite, Palygorskite, Prehnite, Pumpellyite, Pyrite, Quartz, Ruizite, Scolecite, Stilbite, Stringhamite, Tacharanite, Thomsonite, Tremolite var. Byssolite, Tuperssuatsiaite, and Whelanite.