Natrolite

Natrolite from Cairns Bay, Flinders, Victoria, Australia, measuring 75 × 55 × 52 mm and weighing 132 grams. A chunky, roughly cubic piece showing this classic Victorian zeolite on its own, without the other species that often share its cavities.

Natrolite is a sodium aluminosilicate zeolite, Na2Al2Si3O10·2H2O, and it is probably the single species most associated with Victoria's basalt zeolite localities. It crystallises in the orthorhombic system, almost always as slender, acicular crystals gathered into radiating sprays or felted masses, and good examples can show a faint silky sheen where light catches the bundled needles. It is named from the Latin natron, for sodium, reflecting its place as the type sodium zeolite described in the group.

Cairns Bay's basalt, part of Victoria's Older Volcanics, has vesicles and fracture linings that formed as gas bubbles and cracks in the cooling lava were later filled by zeolites precipitating from circulating groundwater. A clean, single-species Natrolite like this one is a good reference piece for anyone wanting to see the mineral at its most typical, and it comes from the David Vince Collection, a source that has brought a good run of Victorian zeolites to market over the years.