Heulandite

This is an attractive group of lustrous, orange, diamond-shaped crystals arranged in radiating sheaves. Heulandite is in the group of minerals called ‘zeolites’, from Greek words meaning ‘boiling stone’, as they froth and bubble when intensely heated. Zeolites have an unusual interior structure of parallel channels which makes them useful as molecular filters. This zeolite has the composition of calcium, sodium, potassium, aluminosilicate with water.

The zeolite mineral deposits in the Coonabarabran region north-west of Sydney were first discovered by Colonial Geologist Samuel Stutchbury in 1863. These zeolite minerals formed in hot spring waters that bubbled up when volcanoes were erupting in the area in Jurassic times, 150 million years ago. The orange-coloured heulandite and stellerite were accompanied by analcime and drusy quartz within cavities in basalt. Oliver Chalmers in the Museum’s Mineralogy department went on an expedition to this area in 1933 and collected many samples of zeolites. Nice specimens can still be found, mainly on Portobello, Glendowda and Garrawilla Stations.

Albert Chapman acquired this specimen from mineral collector John Wolff who obtained it about 1975.

Portobello Station, near Coonabarabran, New South Wales, Australia. 10.5 x 8 x 4.3 cm. D.50661. Albert Chapman Collection.