I'm delighted to give the floor to Geoff Winkler, who's building a bluestone house in southern Victoria. He has direct experience with the various properties of stone at first hand... This is a very different kind of knowledge/obsession: very practical and intimate knowledge. Click through to the photos of his house.
Thanks to Geoff, and best wishes for his building project.
BLUESTONE AIN’T
BLUESTONE
Most Melbournians’ perception of bluestone has been gleaned
from seeing it in its most common use as paving and building stone. Rock for
this purpose was usually quarried from one of the many deep deposits over the
western and northern parts of the greater metropolitan area.
In the thicker beds, where the lava flows cooled very slowly
and uniformly, the contained gasses rose to the surface. This led to the texture
of the basalt becoming very even and fine grained. Generally, this is regarded
as the best quality stuff for the building industry, however, the range of variations
in bluestone is actually quite diverse.
I have always had a great fondness of bluestone myself, so
much so that in 1994 I embarked on the biggest undertaking of my life, building
my own stone
house at Bellbrae, in southern Victoria. I greatly underestimated the
logistics involved and subsequently also set about
building a saw to
assist with the project. I have sourced the raw stone from many nearby
localities and from as far afield as Stoneyford, near Camperdown.
When I’m sawing the raw stone into usable blocks, many different
textures and features are brought to prominence. Some of these examples I share
with you here. The muddy water produced in the process is also quite
interesting and varies quite considerably. The spectrum runs from a “clean”
deep blue/grey colour from the Warrion Hill stone, through rusty reds from high
iron content stone sourced from Lovely Banks, to “dirty” browns from Mount
Duneed and Winchelsea. By “clean”, I mean that the sediments tend settle very
quickly, whereas with the “dirty” the water stays cloudy and mucky for quite a
considerable time.
Pic
1 
A Common feature in the finer grained bluestone is “Veining”.
This is where bands of gas bubbles, or “Vesicles”, have become entrapped as
successive layers of lava have been overlain.
Pic
2 
Also quite common is what’s commonly known as “cat’s paw”.
It can occur in a similar fashion to veining, where rounded groups of vesicles
are entrapped, or when fragments of already solidified lava are melded into the
mass, as in this case.
Pic
3
When the lava cools more rapidly, generally in the thinner
and more erratic flows, or nearer to the surfaces on the thicker deposits, the entrapped
gasses are unable to escape and remain in situ. In this state, the basalt is
termed “Vesicular”, or as it’s known to more common people like myself,
“Honeycombed”. This is the most abundant form of readily accessible bluestone
in Victoria and is found right across the Western district and at least as far
north as Bridgewater (on Loddon). The composition and textures vary quite
considerably though. Despite it being not generally highly regarded,
historically in the building industry, its appeal grew on me and I now much
prefer it for a rock faced surface finish. I feel it has a much more “natural”
look about it. This sample, from near Beeac and typical of the flows from
Warrion hill, has a very even texture and little in the way of “impurities” and
“fracturing”. This stone was used in a number of local buildings there and its
only downfall, in the one case that I’m aware of, resulted from inadequate
footings.
Pic
4
From a little further west at Mt Pollock, near Gnarwarre,
this piece has small amounts of other minerals crystallizing inside the vesicles
and forming small nodules. These commonly include quartz,
calcite (calcium carbonate) or other minerals called zeolites. It is a similar phenomenon to that which
occurs in the formation of “Geodes” found in sedimentary rock, where the
crystallisation tends to occur evenly all around the void. In all the examples from
within basalt that I have seen however, it tends to form from the bottom. This
makes it easy to determine the original orientation of any basalt containing
it.
Pic
5
This “Vein”, contained in a piece from a small outcrop near
Winchelsea, was exposed when splitting the rock along the same plane. Most of the
vesicles were nearly filled entirely with Quartz. When this occurs and the rock
assumes a more solid mass, it is referred to as being ‘Amygdaloidal’.
Pic
6
Mt Porndon near Stoneyford produced this interesting
example, the nicest I have yet come across. Where a wide, but shallow, fully
enclosed “Vug” (void), was formed within the flow, the crystallizing Quartz
formed within it has the appearance of a coral garden.
Pic
7
Other rocks can also found in Basalt as inclusions, these
are formally termed “Xenolith(s)”. This is where pre-existing fragments have
been incorporated into the molten lava. This sample contains, what appears to
be, a lump of quartz.
Pic
8
The correct term used to describe the small white flecks in
this sample, from the earlier flows surrounding Mount Porndon, is that it
contains “plagioclase phenocrysts”. It sounds a bit brain numbing, but the word
“plagioclase” refers to a form of ‘feldspar’, which is part of a group of
minerals that make up as much as 60% of the Earth's crust.
“Phenocryst” refers to their conspicuous crystal size, being distinctly larger
than the grains of the host rock.
pic
9
Basalt found on the flanks of Mount Duneed, south of Geelong
is about the crankiest stone I have worked with. It is a paler grey colour and
the vesicles, generally flattened, show no consistent orientation. They swirl
in all directions and vary considerably in size up to some quite large voids.
Foreign inclusions (Xenoliths) are many, the stone is more brittle and stress
fracturing is common.
I didn’t set out to be too technical with the terms used
when writing this, but as the subject is investigated further, I am finding it
increasingly difficult not to do so. An almost unlimited number of variations
exist that I have not seen myself as yet. One that I would particularly like to
witness is the relatively large Olivine inclusions, apparently quite common in
the lava flows from Mt. Shadwell, in the Mortlake area. I intend to continue
documenting my observations and will hopefully be able to provide further
updates.
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