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.
|
