Australian unique ‘Zebra Stone’ specimen, NT

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Zebra Stone

Ranford Formation,

East Kimberly, Northern Territory, Australia

10x8cm

This amazing natural stone is only found in a small location in Northern Australia. It is a ‘silt-stone’, the result of sediments of fine quartz and iron stained minerals being deposited at different times, in starkly different colours. The exact process has never been absolutely explained; officially recorded as “the rhythmic precipitation of well defined, hematite rich liesegang bands in selected parts of the siltstone, caused by the percolation of warm hydrothermal fluids or other chemical activity during a period of alteration of the rock” .  In other words, a sediment in a lakebed altered by seasonal change, with well spaced grooves opening and being filled with the iron rich minerals. These minerals may have come from periodic volcanic activity.
An alternate theory involves bacterial colonies filling ripples left in sediment on the bed of a lake, which in turn allowed the different mineral to penetrate and form ‘stripes’. This is also an elegant way to explain the iron-stained brown colour, as bacteria can accumulate iron while living and leave a trace as a fossil record.

Whatever the development process, it allowed a different coloured mineral to penetrate in a uniform manner, resulting in the remarkable stripes when cut.

The age of the formation it is part of is dated to around 600 million years ago, during the Ediacaran Period.

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