On Sunday, 22nd October, 1995, Heather Bildstein led members of the Mineralogical Society of Tasmania to a dolerite quarry, located about 3kms past the bridge over the Russell River near Judbury, in southern Tasmania. There was a good turnout of members for what was the first trip to this quarry, and the weather was fine for the whole day.
Heather's description of "lots of white crystals" turned out to be mainly veins of calcite and various zeolites, occurring in faults and shrinkage veins, typical of Jurassic dolerites throughout the southwest. One boulder in particular, where there was an abundance of white calcite crystals on one face, had eluded Heather's attempts at removing a specimen on past "bushwalking" visits. This time around, with the help of strong arms and heavy hammers, a specimen or two was extracted to add to Heather's collection.
There were plenty of tadpoles to keep the kids happy, and specimens of varying sizes could be found to suit most tastes, and keep the big kids happy. A short stint after lunch was topped off with a stop off at the Judbury picnic area for some, before heading home. In all, a pleasant and productive day, amongst good company. Thanks go to Heather for leading the trip.
The Minerals
Bitumen. Although not classed as a mineral, finding bitumen, apparently occuring naturally, was a suprise. It occurrs as black elastic masses in calcite veins, in what looks like unweathered dolerite boulders. Various possible sources were discussed, from someone tipping over a 44 gallon drum, to the occurrence of (long since removed) coal or oil bearing rocks above the dolerite. Ralph has taken some specimens to test.
Calcite. Found mostly as abundant colourless to white scalenohedral crystals, generally up to about 1cm in length. A few specimens were found with much larger crystals, where they had grown along veins instead of across. Many specimens were sprinkled with small pyrite crystals.
Chabazite. Occurs as untwinned rhombohedral (pseudocubic) or simple interpenetrant twinned crystals to a few millimetres across, usually associated with stellerite. Often, specimens look pale green, probably caused by transmitted colour from the underlying rock.
Heulandite. Confirmed by XRD.
Laumontite. Not common, found as white masses.
Pyrite. Small, usually less than 1mm, slightly modified cubes occur generally on calcite or stellerite. A few much larger crystals and masses were found.
Stellerite. Stellerite forms mostly as colourless drusy coatings of fractures in the dolerite. The morphology is the typical flat topped prism.
Stilbite. A small number of specimens exhibited a stilbite-like morphology, with these crystals generally larger than the stellerites. It's occurrence has not yet been definitely confirmed.