Si02; A mineral used in making glass (6)

I believe the answer is:

silica

(Other definitions for silica that I've seen before include "Oxide occurring as quartz and used in making glass" , "Common base of rock" , "Eg, quartz" , "Hard colourless compound from rocks" , "Quartz used in the manufacture of glass" .)

I've seen this clue in the Sydney Morning Herald.

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