Thin sections of “Cold Moor Ironstone”. 

Sample taken from trial adit on west side of Cold Moor.

Top two photo’s are in plane polarised light (PPL). and cross polarised light (XPL).They show bioclastic debris within a matrix of siderite with a dark patch  in the upper part showing  part of a phosphatic nodule interestingly enclosing two chamosite? ooliths.  The characteristic concentric structure of the ooliths  is visible in XPL as well as the extinction cross. (For scale the lower oolith is ~1mm width, left to right.)


Bottom two photo’s are from a different part of the thin section. The rock is dominated by bioclastic debris within a matrix of siderite. Scattered quartz grains are visible, showing grey interference colours. According to this thin section the rock would be described as a bioclastic ironstone with phosphatic nodules. The bioclasts have been interpreted as echinoderm and coral debris. The sample was taken from the trial adit on the west side of Cold Moor (about NZ550 032)

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