Apophyllite

Apophyllite is the collector's name for a group of hydrous potassium calcium silicates crystallizing in the tetragonal system, now formally split by the IMA into fluorapophyllite-(K), hydroxyapophyllite-(K) and fluorapophyllite-(Na), though the traditional name remains standard in the trade. It typically forms pseudocubic, blocky or tabular crystals with a perfect basal cleavage that gives a distinctive pearly-to-vitreous luster on that face, quite different from the glassy luster on the prism faces. Color ranges from colorless and white through pale yellow and pink to the prized emerald-green, vanadium-bearing crystals that made Indian material famous worldwide.

The single most important source is the Deccan Traps basalt province of western India, where amygdaloidal cavities have produced the world's finest specimens for decades. Classic localities include the now-closed Pashan Hills quarries near Poona (Pune), source of deep emerald-green crystals on pink stilbite, and the more recent Jalgaon district, which has yielded gemmy green apophyllite of comparable or superior quality, often accompanied by heulandite, mesolite and stilbite. Nasik and Mumbai (Bombay) districts round out the Indian production, occasionally combined with cavansite and powellite from nearby occurrences. Outside India, exceptional apophyllite has come from the trap-rock quarries of Paterson and the Millington Quarry in New Jersey, USA, where pink and colorless crystals grow with datolite and quartz; from the historic silver mines of Kongsberg in Norway; from Andreasberg in Germany's Harz Mountains; and from Guanajuato, Mexico, each producing habits and colors distinctive enough to be recognized by experienced collectors at a glance.

Collectors seek apophyllite both as an affordable, widely available species for study collections and, at the high end, as one of the most aesthetically striking combination specimens in mineralogy: sharp, lustrous, water-clear or richly colored crystals perched on contrasting beds of pink or peach stilbite, white heulandite, or fibrous mesolite. Fine Indian green apophyllite with vanadium coloring, or large, gemmy, doubly terminated Jalgaon crystals, can command prices reaching into the thousands of dollars, while classic old Poona pieces from now-inaccessible Pashan Hills workings are prized as historic, no-longer-obtainable material. Its softness and easy cleavage make it a delicate but visually rewarding centerpiece for any zeolite or Indian trap-rock mineral collection.