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A neck of trachyandesite
The pyramid shape volcanic structure of Puy de Sancys’ summit (6,187 feet / 1,886 metres) is formed by a clear trachyandésite neck composed of large sanidine phenocrystals. The trachyandésites of the Puys Chain – of which the Volvic stone is one of the best examples – are linked to intra-plate volcanism. Its main varieties are domite – which makes up the Puy de Dôme, doréite – associated with the Monts Dore, and sancyite, eponymous of Sancy.
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