Obsidian: Rocks we know we knowDec 21, 2017
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A hard turbidite sediment formed 420-360 million years ago (late Silurian to Devonian).
A turbidite sediment formed by underwater slumping of the sediments and subsequent rapid transportation of the sediments off the continental shelf. The resultant sediments are include rocks such as greywacke, sandstone, shale and conglomerates. Turbidites are characterised by layering with coarser fractions at the bottom and finer fractions at the top of the profile. This can be repeated due to multiple deposition events so you end up with what looks like coarser fractions sitting on fine ones (confusing/revealing). The sediments of the Hodgkinson Basin were up to 10km thick. Toward the edges of this basin, limestone deposits to the west of Cairns around Chillagoe developed from ancient coral reefs off the old coast.
Images are examples of specimens only.
Size and shape may vary.
Specimens are usually no smaller than 150mm in at least one dimension.
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