Gmelinite-Na with Analcime

Gmelinite-Na with Analcime from Cairns Bay, Flinders, Victoria, Australia, measuring 75 × 41 × 40 mm and weighing 121 grams. A neat, manageable piece of the species Flinders is best known for.

Gmelinite-Na is the sodium-dominant member of the Gmelinite series, Na4(Si8Al4)O24·11H2O, and the suffix tells you which cation leads the chemistry. Its typical crystals are hexagonal plates and pyramids, and at Flinders it is recorded with Analcime, Natrolite and Montmorillonite in the vesicular basalt. The sodium needed to grow Gmelinite-Na and Analcime together came from the groundwater circulating through the basalt after it cooled, so assemblages like this tell you a little about the fluid chemistry in that part of the flow.

Flinders has a strong reputation for Gmelinite, and it is the Australian locality collectors most often name for the species, with Cairns Bay one of the documented sites along that coast. Gmelinite-Na is one of the more sought-after Victorian basalt zeolites, and a documented Cairns Bay example carrying David Vince Collection provenance is a sound choice for a Victorian suite.