Tasmania's landscape and geology is dominated by dolerite , a hard & heavy granite-like rock formed by extrusion of magma and subject to complex faulting and other stresses over millions of years. There are many variations , and famously this rock ( aka bluestone)  was used to construct the inner circle of stones at Stonehenge. Dolerite weathers spectacularly, revealing cliffs and columns which are not just aesthetically pleasing but provides home to numerous wildlife species (mostly birds and reptiles) . It also provides excellent sport for rockclimbers!

It weighs around 85kg per cubic foot. That may confuse young people and some of my friends in the states. I have lived through decimalisation in Australia and have no trouble flicking between systems. Try this if you must http://www.convert-me.com/en/convert/weight

Pictures below taken within sight of home...Cathedral Rock & Mt Wellington "organ pipes".



David Leaman, an outspoken and now retired Tasmanian geologist , has written the definite guide to dolerite "The Rock Which Makes Tasmania". Whilst this is a compendium of scientific information and definitely for enthusiasts only ,  he has presented a critical review of the difficulties associated with this rock and the economic cost of underestimating its belligerence.


It is hard & expensive to drill and unlike sedimentary rocks difficult to cut as there is usually no predictable cleavage plane. It's properties mean it is useful for roadfill and gravel . As a building stonecit is hard to come by good freestone i.e. stone which has already cleaved or can be worked into straight-sided pieces.

If you try to shape a piece with a sledgehammer , most likely it will splinter into uneven lumps , that is if your blows are even successful at breaking it at all. The shards will cut fingers and lodge in your eye.

I once spent an hour drilling through a river stone with a water-cooled diamond tipped drill bit . Just so I could thread a hook into the stone for lifting purposes.

It is a mean-spirited and imposing rock. But it is tough and you can throw it around with impunity. There is a lifetime guarantee, as long as the rock has not been burnt in a bushfire...

Dolerite stones are dense and good lifting can be had from relatively small stones. Long stones are robust , whereas long sandstone breaks easily when dropped. Smooth river stones can be a devil to lift, and it is an unwise man who tries to lift a heavy one overhead. On the other hand weathered dolerite provides excellent grip. The negative is that foreams can take a beating, and bushfired rocks may fracture unexpectedly. Once again I do not try to lift these overhead.

Iron-rich weathered dolerite (from my Dragon's tooth stone in the large stone circle)



Landscaping with dolerite can be highly frustrating or highly satisfying and sometimes both! It is extremely hard to build walls with weathered boulders due to their tendency to form rounded edges and the difficulty splitting them. Splitting also reveals fresh bluestone which in my opinion is not as attractive as weathered stone. Lichen on the rocks makes them especially attractive, and are a feature of many mountains and parts of the coastline. Near Hobart , greens prevail at lower altitudes whilst higher up the lichens are almost exclusively orange.


Lichens are composed of fungi and algae in a symbiotic relationship. Here is a good link if you are interested. http://www.dec.wa.gov.au/science-and-research/plant-research/lichen-info-sheet.html

"The fungus provides support and anchorage, absorbs water and helps to obtain mineral nutrients by breaking down surface material. The algal (or cyanobacterial) partner photosynthesises, converting energy from the sun to produce food for both partners."

http://en.wikipedia.org/wiki/Lichens

Lichens are tough and have survived unscathed after 15 days in the vacuum of space!
These are growing strongly on our block.