Mordenite

Mordenite from Bombay, Maharashtra, India, measuring 124 × 83 × 60 mm and weighing 602 grams.

Mordenite is a fibrous zeolite that, like Stilbite and Heulandite, crystallises in the gas cavities of basalt long after the lava itself has cooled, and the Deccan Traps basalt flows around Bombay are one of the world's most productive sources of this kind of cavity zeolite mineralisation. Mordenite typically forms fine, radiating or felted fibres lining a cavity wall, often alongside the better-known Deccan zeolites, and a piece of this size, at over 600 grams, gives a good sense of how substantial the cavities in this basalt can be.

This specimen comes from the David Vince Collection. A large Indian Mordenite like this one is a solid representative piece for anyone collecting zeolites from the Deccan Traps, one of the richest basalt mineral provinces anywhere in the world.