Chabazite with Ferroan Calcite

Chabazite with Ferroan Calcite from Boral Quarry, Bundoora, Melbourne, Victoria, Australia, measuring 55 × 51 × 40 mm and weighing 85 grams.

The rhombohedral Chabazite here is accompanied by Calcite carrying enough iron substitution to be described as ferroan, a variety that can show a subtle colour shift compared with pure Calcite depending on how much iron has entered the structure. Both minerals crystallise from groundwater moving through the gas cavities of this Bundoora basalt long after the lava itself cooled, with the iron content of the Calcite reflecting the particular chemistry of the fluids reaching this part of the flow.

This piece comes from the Allan Waldon Collection. It's another good example of the variety this one quarry can produce, and a useful comparison piece alongside any plain Calcite or Chabazite already in a Victorian zeolite suite.