At the GZ you will find an outcrop of rocks that are common in this reserve. The outcrop consists of Mica-Schist, which is very distinctive because of the shiny mica within it, and Gneiss, which consists of layers of a variety of minerals. Both mica schist and gneiss are Metamorphic rocks that have been formed under immense heat and/or pressure within the earth.
The big difference between the two is the Gneiss does not fracture along the planes of the mineral streaks within it. Mica schist does and this means pioneers in the area frequently used this rock in the construction of houses and other structures as the rock broke along flat planes, making it easy to use it as a building material.
When we see an outcrop like this it is interesting to speculate as to why it is here and why have the rocks been weathered into the shapes that can be seen. While wind, rain, ice and even surrounding plant material can influence the type and rate of weathering there are two important elements that really determine the shape of any landform......
Structure ....... this refers to the cracks or joints within the rock. After the rock has been formed it is then subject to forces within the earth (tectonic movements) that can form seemingly random or patterned cracking of the rock. These cracks alow moisture to enter the rock to begin the weathering process. The greater the amount of cracks or joints the greater is the surface area exposed to weathering forces. On the central Eyre Peninsula there are landforms known as Inselbergs (island mountains) that rise up abruptly above the surrounding plains. Investigations have found the same granite under the soil of the plains however far more joints/cracks has meant this rock has worn down faster, leaving the Inselbergs such as Mount Wudinna or Pildappa Hill, as remnants of the old landscape.
Composition ....... Most rock outcrops consist of a number of differing minerals. Each may differ considerably in hardness and therefore wear away at different rates. Some rocks, such as talc or chalk, are very soft while others like limestone can be relatively easily broken down in water. easily be broken down in water. This accounts for the "honeycombing" of the limestone cliffs along the Murray River. On the other hand Granite is particularly hard although even within that rock the three minerals, quartz, feldspar and mica, are all of varying hardnesses and can weather at differing rates.
Look closely at the rocks at Ground Zero. Look out for variations in rock types that might have influenced weathering rates. Look out as well for cracks and joints that may have opened up parts of the rock to faster rates of weathering.
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1. Is there evidence of layering within the rocks at the GZ? If so what is the thickness of these layers?
2. Look at the largest rock at the GZ. Is there any evidence that the cracks in the rock have been opened up by weathering process?
3. Describe the appearance and texture of the shiny rocks (mica schist) and of the lightest coloured rock material within 5 metres of GZ.
4. Provide a scientific or creative explanation as to why this outcrop is here!
5. Having examined the area... what do you think? Was rock structure or rock composition more important in forming this outcrop?
If you approach this location via the most direct route the terrain rating is 3.5. If you want an easier approach (T=2.5) look at the satellite photo of the area and follow the track around so that you can enter the scrub from the south.