Wednesday 30 November 2011

To the geologist a road cutting is a tourist attraction!

I dont know where this came from as it was sent to me in an email but it is so good I had to reproduce it... well good as far as geological humour goes!

You know if you are a geologist if:

  • You can pronounce the word "molybdenite" correctly on the first try.
  • You think the primary function of road cuttings is for a tourist attraction.
  • You associate the word "hard" with a value on Moh's scale instead of "work".
  • The pile of rocks in your garage is taller than you are.
  • you have a strong opinion as to whether pieces of concrete are properly called "rocks".
  • The local university's geology department requests permission to hold a field trip in your back yard.
  • There's amethyst in your aquarium.
  • Your wife has asked you to move flats of rocks out of the tub so she could take a bath.
  • You spellchecker has a vocabulary that includes the words "polymorph" and "pseudomorph".
  • You think Rocky, Jewel and Beryl are good names for your children.
  • You were the only member of the group who spent their time looking at cathedral walls through your hand lens during your last trip to Europe.
  • Work wont give you time off to attend the national gem and mineral show and you go anyway.
  • You begin fussing because the light strips you installed on your bookshelf is not full spectrum.
  • You've purchased an individual, unfaceted rock, regardless of the price.
  • You've ever spent more than $50 on a book about rocks.
  • You shouted "Obsidian!" while watching "The Shawshank Redemption".
  • You find yourself compelled to examine individual rocks in driveway gravel.
  • The Geological Survey identifies your rock collection as a major contributing factor to isostasy in your state.
  • You know the location of every rock shop within 2 hours drive of your home and when they haven't seen you for a week the shop owners send you get well cards.
  • You have retired but are still thinking you need another room on your house for your collection.
  • You get annoyed when people think you are talking about petroleum when you are discussing matters about petrology.
  • Your idea of a "quiet romantic evening at home" involves blue mineral tack and thumbnail boxes.
  • You plan to use a pick and shovel while you are on holiday.
  • You can point out were Tsumeb is on a world globe.
  • You associate the word "saw" with diamonds instead of "wood".
  • You consider a microscope useless unless it has polarising lenses and an accessory plate.
  • You begin wondering what a complete set of the Mineralogical Record is worth and when you find out you actually consider paying for it.
  • you've installed more than one mineralogical database program on your computer.
  • You throw out clothes instead of rocks to keep the weight of your baggage down before checking into your flight.
  • You receive a letter from the local council informing you that you will need a landfill permit if you place any more rocks on your property.
  • Your internet home page as pictures of your rocks.
  • There's a copy of Dana's Manual of Mineralogy next to your toilet.
  • You still think that pet rocks are a pretty neat idea.
  • You get excited when you discover a hardware store that stocks 16 pound sledge hammers.
  • You debate for months on the internet concerning the relative advantages and drawbacks of vibratory versus drum tumblers.
  • Your employer has requested you don't bring any more rocks into the office.
  • You really want to keep the rock on your wife's wedding ring.
  • You know that the word "aa" does not refer to the alcoholic support group.

Thursday 24 November 2011

What is the Mount Warning erosion caldera?

It is very popular to refer to the Mount Warning area as the Mount Warning erosion caldera or Tweed Shield erosion caldera. Many sources indicate that it is the biggest erosion caldera in the world. For example Bigvolcano or good ol' wikipedia use the term. There are some very informative books by top class geologists such as Rocks and Landscapes of South East Queensland by Warwick Willmott also use the term. It is certainly an imposing volcanic influences landscape, but what is an erosion caldera anyway.

Ok. Let us start somewhere definite. A geological dictionary definition. Lets just look at caldera: A large circular crater left after the collapse or explosion of a volcanic cone. Now, lets look at erosion: The wearing away of rocks or other materials by the action of water or ice or wind.

So, Adding the term erosion to the front of the word caldera implies this: a landscape formed through the actions of wind or water or ice but also simultaneously formed through the collapse or explosion of a volcanic cone. Hopefully, you agree that this is possibly misleading. We have two different formation concepts equally applicable at the same time. What gives? How can the same feature form at the same site twice? once by erosion and once from the collapse of a magma chamber.

Mount Warning in the centre of the volcano remnant
Mount Warning was once the centre of a large volcanic cone called the Tweed Volcano. The centre of the Tweed Volcanic cone was a crater which may have collapsed or exploded as some stage to create a larger caldera. But this process is not definitely known because if this caldera actually existed it has since been eroded away to reveal the valley systems that we see today.

I think is is becoming obvious that there has been some sort of mistake in the development of the name erosion caldera. So, why use this term? A short answer is that most geologists tend not use this term, unless informally to illustrate the grand nature of some valleys that are formed in the remnants of large volcanos. That is not to say that some geologists don't mistakenly use the term anyway, I mean even geologists are human!

My suggestion, is not to use the term erosion caldera at all since it often results in confusion on the mechanism for the formation of thing it is actually used to describe.

Sunday 20 November 2011

A rock forming mineral: Olivine

Everyone has heard of the very common mineral called quartz, most people have heard of the very common mineral called feldspar, but surprisingly few people have heard of the very common mineral called olivine. I speculate that this is for two reasons. one being that quartz is resistant to weathering and is very easy to find, feldspar often occurs in big crystals and is also somewhat resistant to weathering, whereas olivine quickly breaks down into clay and occurs in mafic (quartz poor) rocks. the second being that it is often only obvious as large crystals in some basaltic rock.

But firstly olivine is made from similar components as most of the other common minerals. In particular it is comprised of silica with either/or some magnesium (Mg2SiO4), known as forsterite or iron (Fe2SiO4), known as fayalite. Its chemical formula is often given as ((Mg,Fe)2SiO4) because the magnesium or iron can substitute for each other and are usually present together. Because of the nature of the chemical bonds between the magnesium, iron and the silica group the mineral weathers quite rapidly (geologically speaking). Forsterite (mg rich) tends to be an olive green colour and because of the iron content fayalite is more browny-green.

Bowens Reaction Series from Encyclopedia of Earth
Olivine is crystalised in volcanic rocks at high temperatures. This means that as a mafic (basalt like) magma chamber cools the first mineral to form into crystals is olivine (see figure opposite). This indirectly means that if you see olivine crystals in the field it is usually because the rock was a lava that was erupted relatively rapidly to the surface from deep in the earths crust or upper mantle. But, sometimes you can come across rocks that are almost entirely made from olivine. These rocks are called dunite. It is formed at the boundary between the crust and the mantle and has crystalised there. It is thought that it has been bought to the surface through the action of plate tectonics where sometimes large chunks of oceanic crust can be scraped onto a continental plate as the process of subduction takes place. This is called an ophiolite sequence.

A metamorphic source of olivine is through the contact metamorphism of dolomite limestones.


Chemical Formula: (Mg,Fe)2SiO4
Hardness (Moh): 6.5-7
Specific Gravity:
Colour: Olive Green (Forsterite) to Browny-Green (Fayalite)
Luster: Vitreous (glassy)
Crystallography: Orthorhombic
Gem: Peridot
Common accompanying Minerals: Not found with free quartz crystals. reguarly found with feldspar, pyroxene, augite

More information on olivine can be found one the Mineralogy Database.

Just a quick note on dunite and ophiolite sequences, this rock type is named after Dun Mountain in the northern part of the South Island of New Zealand. Dun Mountain is almost exclusively made from dunite and is part of a geological feature known as an ophiolite sequence which stretches along and off the Alpine Fault in New Zealand. Another ophiolite sequence is present in New Caledonia. Closer to home, the Peel Fault which runs along the western side of the New England Tablelands past Tamworth eventually to somewhere near Port Macquarie, also resembles an ophiolite sequence. I will discuss the Port Macquarie part of the Peel Fault at some time in the near future.


*Klein, K. Hurlbut, K. Manual of Mineralogy (After Dana, J.D.). Wiley 21st Ed.
*Encyclopedia of Earth:

Tuesday 15 November 2011

Radioactive paradise (slightly)

The areas of the Tweed Valley, Nightcap National Park and Byron Bay are often seen as fresh clean and natural. Well, I can argue that especially Byron Bay may be a little unnatural but certainly there is a feeling of 'freshness' with the rainforests and the beaches. Given this, few people would think that you'd get a bigger dose of radiation from living in these areas than you would in Brisbane or Sydney (even living near the Lucas Heights Reactor).

Few people realise that radiation occurs naturally in the environments in which we live. Yes, most of you would know that the Sun is a thermonuclear power station bombarding Earth with gamma radiation on a daily basis. But it is also a natural part of the earth and actions either natural or man made can result in these areas being elevated in radiation. In the cases below the sources are formed through different ways but all provide an increase in radiation sometimes thousands of times higher or more than what would be considered background.

Let us look at the little village of Uki first. This little place is located in the Tweed River valley and is known for its rainforest surroundings and rugged, scenic landscapes. Geologically some of the area around Uki is situated on mesozoic aged rhyolite of the Chillingham Volcanics and this rock type provides an added level of radiation due to the minerals that exist naturally in it. But even more interesting is that a mineral exploration company discovered a very tiny sized but significant anomaly in the radiation levels just south of the village. The source was not clear but sampling showed that a five square metre anomaly existed in the already slightly elevated rhyolite terrain background radiation. Analysis showed a nearly 0.05% concentration in uranium which is quite high. This is many thousands of times higher than the normal level expected. The reason for this anomaly remains unknown.

Byron Bay is located on the southern side of expansive active and historic beach systems. Much of the Byron Bay area (and much of the north coast itself) was subjected to heavy mineral mining up until the 1980's but this has ceased now. The heavy minerals sought after were mainly titanium rich ilmanite and rutile and there are other heavy minerals too such as zircon and monazite. These minerals were naturally enriched through the processes of wave and tidal action which created zones amongst the dunes that were targeted for mining. But many of the left over heavy mineral sands were not needed once the rutile and ilmanite were removed. So the left over mineral sand was discarded in some cases used as fill for future building sites. Little did people realise monazite rich left over sand would cause issues which may be unsafe for building homes on. This is because monazite is a radioactive mineral and when the residually enriched sands were dumped this increased the concentration of thorium and uranium and the associated radiation. In fact this situation didn't just occur at Byron Bay but all along the north coast.

More broadly, but less significantly many areas where rhyolite or granite is the underlying rock also have higher than normal background radiation. This too is because of radioactive minerals being enriched naturally when these sorts of magmas are being formed. So this would apply to areas in or close to the national parks of the nightcap ranges and many areas inland in the headwaters of the northern rivers such as the Clarence or Bellinger Rivers and large expanses of the New England tablelands.


 *Pechiney Resources (1970). Report on air and ground prospection, Clarence-Moreton Basin, EL 278, Nimbin - Murwillumbah area. Unpubl. Exploration Progress Report.

Friday 11 November 2011

Coal seam gas gets a seismic thump!

Ok, time for me for foray into an area that is politically sensitive. But I hopefully do so factually.  I'm starting now because of recent developments by the Lismore City Council to first approve a Review of Environmental Factors (Which is strange since the Mineral Resources Division of the NSW Government approves these (or was it approval to use road reserves? I can't seem to figure out what authority the council has from the news reports)) and then to rescind this approval once they found that the work being undertaken could be used to target the area for further coal seam gas exploration (well... that is how I read it). Here are two newspaper reports that discuss the matter: Northern Star and Northern Rivers Echo.

So, I guess the centre of the matter is 'what is seismic exploration anyway?' Seismic exploration comes under the category of geophysics and in this case refers to the use of sound waves to try and understand what is below the ground. It is a non invasive method with the major environmental impacts believed to be limited to noise pollution and a small area of squashed grass. Practically one of the common processes used (and I understand this may have been the method outlined in the REF) is a truck with a pad under which will drop and hit 'thump' the ground. Sensors in the truck (or an accompanying vehicle) then receive data back from the ground as the vibrations made are reflected off layers of rock under the ground. The truck will then drive off a hundred or so metres further along and then do it again and so on.

The Department of Mineral Resources have previously conducted some of this work in the area since the 1970s. But I understand that Metgasco are currently undertaking more detailed work which may provide them with information that can lead to (or rule out) possible places to target exploration drilling. The Roads and Traffic Authority (RTA) frequently use this technique when planning routes for roads, the last time I heard this was between Byron Bay and Grafton about 6 months ago.

The decision by Lismore City Council is therefore one I find a little hard to understand unless it is simply a matter of the Councillors not understanding the technique itself or just deferring to the current political environment. Personally, I'd certainly love to get some more geophysical information on the Clarence Moreton Basin (for the sake of scientific knowledge itself) since I've recently had some discussions various people that prove that we know very little about faults, stratigraphy, intrusions, groundwater, deformation, metamorphic events, etc that have occurred in the basin since the rocks were laid down. Seismic exploration would go along way to answering some of these questions. But I guess if the politicians and general public don't want the information to be used specifically in coal seam gas exploration then it is important that we do not learn about these features in our region. That might be a price many in our region are prepared to undertake.

Tuesday 8 November 2011

The volcano of the Border Ranges - Focal Peak

I was going to do a blog on the Focal Peak Volcano and the Cenozoic aged volcanic rocks associated with it in the Northern Rivers/New England NSW but to get an understanding of these rocks on the southern side of the dotted line you really have to know a bit, or a lot about the geology across the border. With that in mind I was going to write this blog but then I remembered that the wonderful Queensland branch of the Geological Society of Australia have some excellent information sheets on Mount Barney and Mount Barlow that would do just the trick. So instead of starting from scratch I thought I'd just link directly to the PDF. Here it is.

The authors of this information sheet are Neville Stevens and Warwick Willmott who in my view are/were some of the best science educators in the country and happen to be geologists! I have enjoyed some of their presentations (and many others) at the Theodore Club in Brisbane when I lived there and it is one of the things I do miss about living away from that city. Alas, Neville passed away earlier this year.

While I'm talking about Queensland I should recommend a couple of books which gives an excellent account of the geology of Southern Queensland these are Rocks and Landscapes of the National Parks of Southern Queensland by Warwick Willmott and Rocks and Lanscapes of the Gold Coast Hinterland by the same author. I understand this Gold Coast one has just been revised and expanded. You can get a copy of the Southern Queensland one for less than $25 and the Gold Coast one for less than $15 including postage from the Queensland Division of the Geological Society of Australia. For details on ordering these books click here.

Friday 4 November 2011

Ground water in the Alstonville Plateau

A palaeosol in the Alstonville Basalt
Ground water is a valuable source of water for stock watering, domestic uses, irrigation and town water supply in the area of the Alstonville Plateau. For example both Ballina Shire Council and Rous Water operate ground water bores as sources of water for municipal use. The reason for the popular use of the ground water from this source is its yield and also freshness. The quality of the water in the aquifers is excellent and the quantity good. In fact the popularity of ground water from the Alstonville Plateau is such that it threatens to be over used with many aquifers being badly drawn down and for this reason the NSW state government has put in place a water sharing plan that prohibits new water extraction licenses from some areas of the plateau and all ground water bores in the area require a license.

So what is the Alstonville Plateau ground water source anyway. Where does the water come from? Well, in short, the Alstonville Plateau ground water source is a series of aquifers that occur in the Cenozoic basalt that defines the area of the Alstonville Plateau. The plateau extends from beyond? Lismore in the west almost to the coast at Lennox Head, past the little village of Newrybar in the north (almost to Bangalow) and south almost to the Richmond River at Broadwater. According to Brodie and Green (2003) there are several aquifers with the upper most being an unconfined source of water within the upper weathered and/or fractured zones of the basalt. Below this is at least one confined aquifer which flows through permeable layers such as paleosols (old soil horizons) or through fractures in the basalt. An example of a paleosol from the Alstonville Basalt is shown above (not acting as an aquifer in this case).

The unconfined aquifer is usually able to be intercepted within several metres of the surface but this depth can vary wildly depending on the depth of soil weathering zones and local topography. This shallow source is usually easy to find but yields are usually low and are often subject to drying out during periods of drought due to the local surface water influence on these aquifers. In general when it rains the streams tend to recharge the aquifers and when the weather dries out the aquifers tend to return base flow to the streams (until the aquifers run out of water).

The deeper aquifers are confined between layers of basalt. The layers that the water is found in is either made from substantially fractured rock or paleosols that were developed on lava flows and were subsequently covered up by new lava flows (i.e. are directly related to the eruptive conditions during the formation of the basalt). Interestingly, the dip direction of the aquifers is generally from east to west which is somewhat inconsistent with the idea that these rocks were sourced from the Tweed Volcano which is the established theory since Duggan and Mason published their paper on the volcanic rocks of the area in 1978.

The interesting thing about the importance of this ground water source is that despite the area being mapped as Lismore Basalt  most other areas of the Lismore basalt away from the Alstonville Plateau are not in as high demand for ground water as the Alstonville Plateau. Why is this? It is possible that there are peculiar features of the plateau such as extensive paleosols but it is possible that it is related to the plateau being derived from an older basalt unit that was identified by Cotter (1998) but has not been followed up in detail by any other authors since. See my older posts on this subject here and here.


*Brodie, R.S. & Green, R. 2002. A Hydrogeological Assessment of the Fractured Basalt Aquifers on the Alstonville Plateau, NSW. Australian Bureau of Rural Sciences, Australia
*Duggan, P.B., Mason, D.R. 1978. Stratigraphy of the Lamington Volcanics in Far Northeastern New South Wales. Australian Journal of Earth Sciences V25.
*Cotter, S. 1998. A Geochemical, Palaeomagnetic and Geomorphological Investigation of the Tertiary Volcanic Sequence of North Eastern New South Wales. Masters Thesis, Southern Cross University.