Unimpeded growth of k-feldspar megacrysts in granitic liquids

R. H. Vernon*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

1 Citation (Scopus)


Though K-feldspar megacrysts are generally regarded as normal phenocrysts, some petrologists have suggested that megacrysts nucleate too late in the duration of crystallization for sufficient unoccupied liquid to be available for the growth of large crystals. Instead, they have proposed that megacrysts grow by "textural coarsening", involving solution of small crystals and deposition on larger crystals, owing to "thermal cycling", in response to repeated magma chamber replenishment late in the crystallization duration. This process could contribute to the grainsize of euhedral, zoned K-feldspar megacrysts only at the stage when megacrysts are free to grow in liquid. However, this process is not necessary for the development of megacrysts because, though K-feldspar saturates typical granitic magmas late in the nucleation (saturation) sequence, plenty of liquid is available for the growth of large crystals. So, though K-feldspar typically nucleates late in the sequence of mineral nucleation, it grows throughout most of the crystallization duration. Abundant structural evidence in granitoids is consistent with free growth of K-feldspar megacrysts in liquid.

Original languageEnglish
Title of host publicationFeldspar
Subtitle of host publicationMineral Composition, Geology and Petrogenesis Significance
EditorsFrancis D. Whitmore, Jorge B. Escamilla
Place of PublicationNew York
PublisherNova Science Publishers
Number of pages15
ISBN (Electronic)9781629486482
ISBN (Print)9781629486475, 1629486477
Publication statusPublished - 2014

Publication series

NameGeology and Mineralogy Research Development
PublisherNova Science Publications


  • Granitoid
  • K-feldspar
  • Megacrysts
  • Nucleation
  • Unimpeded growth


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