| Travelling Australia Fact Sheet http://www.travelling-australia.info |
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| Siltstone at Twofold Bay, NSW. | |
Siltstone is a fine-grained sedimentary rock composed mainly of silt-grade material intermediate in size between
sandstone and shale but not as common as either of these. Siltstone is a product of semi-quiet depositional
environments. The reddish siltstone around Twofold Bay has been coloured by ash from a large number of volcanoes active in
the area when the siltstone was being laid down.
 The Encyclopaedia Britannica defines siltstone as hardened sedimentary rock composed primarily of angular silt-sized particles (0.0039 to 0.0063 mm) and not laminated or easily split into layers. Sandstone is a sedimentary rock made from small grains of the minerals quartz and felspar cemented with calcite, clays and silica. Grain sizes are from 0.1 mm to 2 mm. |
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