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  • The Hammer April 2018

  • The Gstt

    - 29th November 2021

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Scanning Electron Microscopy (SEM) photomicrograph of partially recrystallized diatom frustules, micro pores and interlocking microquartz matrix within siliceous facies of the Naparima Hill Formation at San Fernando Hill. Siliceous organisms (opal-A) may have furnished the major source of quartz within the rock by the solution-reprecipitation process of opal–A to opal–CT and finally to quartz (chert). Chert textures photographed here are not related to the diagenetic replacement of calcite with silica (nodular chert). This rock provides evidence for the formation of biogenic chert textures within sediments deposited above the calcite compensation depth (CCD), within environments with limited terrigenous input and within sediment that contains significant quantities of opaline skeletal remains.