This is a photograph of Uluru, in the Northern Territory of Australia, on a hot and humid summer afternoon. As lightning flashed about, torrential rains swept across the landscape and silver rivulets of water began to rush down the sides of the mountain. Uluru is made of red-coloured Proterozoic arkosic sandstones, a coarse grained lithology rich in quartz and feldspars. However, on rare days such as this, the storm clouds and moisture in the atmosphere filter out much of the red end of the light spectrum and make the rock appear purple.
By Prof. John Clemens, University of Stellenbosch
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