Tertiary basalts outcrop over a large area in the vicinity of Gads Hill which lies between Mole Creek and Moina in the northwest of Tasmania. Zeolites and other minerals occur in vesicles ranging in size from a few millimetres to many metres. Two occurrences of note were reported by Anderson (1984), one, a cavern measuring 8m by 3m by 1m (yes metres!), the second, 5m by 2m by 1m. Crystals of chabazite and phillipsite lined these caverns.

Anderson reports that the zeolite deposit lies on the Mole Creek to Sheffield highway whereas Lancaster (1980), reports the Gads Hill deposit as on Olivers Road, a sealed HEC artery, alongside a scenic lookout. On the weekend trip to the Moina district, members of our Society collected specimens near the Lancaster location at a road cutting about 7km down the Lemonthyme Dam road.

The latter trip provided specimens of chabazite, phillipsite, thomsonite and calcite, all of which were recorded by Anderson, and, in addition, a few specimens of analcite were found, the first time that this mineral has been reported from this location. Other minerals recorded by Anderson include levyne, apophyllite, nontronite, tacharanite and tobermorite.

The other discovery of note on this visit, apart from the analcite, was of a number of interesting and unusual habits of thomsonite (note: there are eleven images of thomsonite, not just those linked directly below (begin here)).

The most common form occurs as colourless to grey, yellow, or brown globular spherules with a pearly lustre. Less commonly, open aggregates of white or yellow flat bladed crystals occur, generally on phillipsite.

There are also two rarer forms, the first as white curved wisps on globular thomsonite, the second as white fibrous masses usually stretching across vesicles with fibres branching out in a number of directions. Both of these habits are reminiscent of some of the thomsonite from Jindivick, Victoria.

A second short visit to Gads Hill on the 3rd May provided some excellent specimens of yellow and brown scalenohedral calcites to 5mm long, chabazite and phillipsite, but very little thomsonite.

References:
Anderson, P. (1984), Zeolites from Gads Hill, Tasmania, in The Australian Mineralogist, Vol 1, p279-281
Anon (1970), Catalogue of the Minerals of Tasmania
Haupt, J. (1989), South Gippsland, in Zeolites of Victoria, The Mineralogical Society of Victoria, p59-65
Lancaster, K.E. (1980), Minerals and Gemstones of Tasmania and their Locations, Gemcraft Publications