How can a nearly pure silica bed with 250 m x 50 m x 1.5 m dimensions be interpreted in a volcanic/pyroclastic setting? Here is a photo of it.enter image description here

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    $\begingroup$ My guess is that this rock is showing evidence of hydro-thermal alteration after the pyroclastic deposit was formed when heated groundwater / magmatic fluids flowed through the rock. $\endgroup$ Mar 4 '19 at 20:50
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    $\begingroup$ What's the stuff above and below the chert? $\endgroup$
    – Gimelist
    Mar 4 '19 at 21:00
  • $\begingroup$ I didn't observed contacting rocks. Note the blocky texture/structure and vesiculates/hollows/holes. The vesicules may transmit thermal waters. $\endgroup$ Mar 4 '19 at 21:58
  • $\begingroup$ Gary, what are the evidences of the rock made you think that it was hydro-thermally altered? What is the degree of the alteration (regarding severity/intensity)? $\endgroup$ Mar 7 '19 at 8:10

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