Natrolite

Natrolite from Cairns Bay, Flinders, Victoria, Australia, measuring 82 × 62 × 26 mm and weighing 122 grams. A neat, fairly flat piece from one of Victoria's classic coastal zeolite localities.

Natrolite is orthorhombic, though its crystals are so nearly square in cross-section that they look tetragonal at first glance, and this is one of the small details that separate it from look-alike fibrous zeolites. Because its structure lacks a centre of symmetry, Natrolite is both piezoelectric and pyroelectric, developing an electric charge under pressure or when its temperature changes. Like the other Flinders zeolites it grew in gas cavities within Eocene olivine basalt, as sodium-rich groundwater circulated through the cooled lava.

The Flinders area has been studied in detail by Victorian mineralogists, including Bill Birch's 1988 work recording the zeolite assemblages of Cairns Bay, and that documentation gives a locality like this real standing. Natrolite from Cairns Bay often carries small amounts of associated Analcime and Thomsonite, a reminder of how closely these zeolites grew together in the same basalt cavities, and this David Vince Collection example comes from that same well-documented setting.