Kaolin or China Clay as it is sometimes known, is relatively pure kaolinite (hydrous aluminium silicate) that fires white with low shrinkage and low plasticity. This clay has a high demand in pottery, paper, refractory and rubber production. It is typically formed by hydrothermal alteration or weathering of feldspathic rocks such as granite.
The clay here forms “drifts” in granite-derived Tertiary sediments of sand and gravel, certain horizons of which are tin bearing. The clay was mined in conjunction with the tin. There are overlying tin-bearing gravels in the northeast of Tasmania (e.g. South Mt Cameron); kaolinised Devonian granite in the northeast (e.g. Tonganah); and weathered Cretaceous syenite in the southeast (e.g. Surges Bay). Production for paper filler has been recorded from Tonganah, South Mt Cameron and Surges Bay. The Tonganah deposits are the only kaolin deposits currently mined in Tasmania, and these produce about 22 000 t of washed kaolin annually for paper manufacture at the Amcor plant in Burnie.
Kaolinite is produced by the chemical weathering of aluminium silicate minerals like feldspar, Granite is a feldspar rich rock and is the source of the Kaolinite in this area. In many parts of the world it is coloured pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations produce white, yellow, or light orange colours and even alternating layers are sometimes found.
Chemical weathering of granite occurs when dilute carbonic acid, and other acids present in rain and soil waters, alter feldspar in a process called hydrolysis. As demonstrated in the following reaction, this causes potassium feldspar to form kaolinite, with potassium ions, bicarbonate, and silica in solution as by products. An end product of granite weathering is grus, which is often made up of coarse-grained fragments of disintegrated granite.
Climatic variations also influence the weathering rate of granites. For example: for about two thousand years, the relief engravings on Cleopatra's Needle obelisk had survived the arid dry conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there.
Soil development from granite reflects the rock's high quartz content, in cool humid climates the weather-resistant quartz produce higher amounts of sand. Feldspars also weather slowly in cool climes, allowing sand to dominate the fine-earth fraction. In warm humid regions, the weathering of feldspar as described above is accelerated so as to allow a much higher proportion of clay.
To log this Earth Cache, we require you to visit GZ and the listed waypoint to make some observations, consider the information given, then message us with the following answers to the best of your ability.
1, Could the climatic conditions this clay deposit formed in be described as Warm or Cold? What effect would this have had on the development of the clay?
2, Look across the lake to the wall, are there any signs of Kaolin, is it the colour you would expect, is it all pure or are there signs of other minerals being present?
3, What is happening to the lake wall?
Make you way down to WP2. Please be aware it is close to the edge of the Lake and there is a drop off, at times the area will be slippery.
4, Describe the colour and the pattern of the clay under your feet here, is it different to the wall? Why do you think this is the case?
5, Find some white Kaolin, rub it between your fingers, describe the texture/consistency, then do the same with the other coloured clay that is present in the area, do they differ, why might this be?
6, A photo of your team or GPS with Little Blue Lake in the background without giving the answers away.
You are welcome to log your find straight away to keep your TB's and Stats in order but please message us with your answers within a couple of days. Cachers who do not fulfil this Earth Cache requirement will have their logs deleted without notice.
Source: Mineral recourse Tasmania, Wikipedia, Minerals education.com