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Taken from 2012-3-14 Quickbridge.
Close-up of the broken down granite - not quite china clay yet!
Some science .....
Kaolin is essentially "rotted" granite where the feldspar crystals have decomposed. Resulted from hot gasses acting on the feldspar when the granite was forming, 295 million years ago in the Late Palaeozoic Era, on the border between the Carboniferous (older) and Permian (more recent) Periods.
Modified from: PZNOW - Penwith's Tors .....
The composition of granite gives it a distinctive appearance. The proportion of the minerals that make up the granite varies from location to location. The main constituents of granite are feldspar, quartz, biotite and muscovite. Also commonly found are pieces of other rock that fell into the granite before it cooled. These are xenoliths. |
Orthoclase (feldspar, colourless) |
KAlSi3O8 |
Good examples of these crystals can seen in some granites. They can be the largest crystals by far. |
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Quartz (white crystals) |
SiO2 |
A very common mineral, the main constituent of granite. |
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Biotite (dark mica) |
K(Mg,Fe)3AlSi3O 10(OH,F)2 |
A black to brown mica, found in nearly all granites. |
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Muscovite (light mica) |
KAl2(AlSi3O10)(OH,F) 2 |
A lighter coloured mica found in granite. |
Wikipedia: Feldspar (an Orthoclase, generally colourless), Quartz (generally white crystals), Biotite (dark mica), Muscovite (common, lighter mica).
For every ton of clay, there are seven tons of waste, now being turned into building materials.