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A porphyritic texture, with large crystals in a fine-grained groundmass, records

  • A.a single stage of very slow cooling
  • B.a single stage of very rapid cooling
  • C.recrystallisation in the solid state
  • D.two stages of cooling, slow then rapid

Answer: D

The magma began to crystallise at depth, growing the large phenocrysts, and was then erupted or intruded to a shallower level where the rest froze quickly. The texture is therefore a history rather than a single condition.

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