Do twinned nuclei promote growth of k-feldspar in granitic liquids?

R. H. Vernon*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapter

1 Citation (Scopus)

Abstract

The very large size of megacrysts in granitoids reflects the relative difficulty of nucleation of K-feldspar in silicate liquids. At least 92% of a large population of K-feldspar megacrysts separated by weathering from a granitoid show simple twinning, supporting observations of typical megacrystic granitoids and trachytes that suggest simple twinning is very common in igneous K-feldspar. This abundance implies that simple twinning strongly promotes the development of viable crystals of K- feldspar in silicate liquids. The similar size of each twin sub-individual indicates twin formation at or soon after nucleation. K-feldspar grown interstitially shows simple twinning much less commonly than K-feldspar grown freely in liquid, probably because abundant crystals are available to act as nucleation substrates. The rarity or absence of simple twinning in the K-feldspar of metamorphic rocks presumably also reflects abundant existing crystals acting as heterogeneous nucleation substrates.

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
Pages77-88
Number of pages12
ISBN (Electronic)9781629486482
ISBN (Print)9781629486475, 1629486477
Publication statusPublished - 2014

Publication series

NameGeology and Mineralogy Research Developments
PublisherNova Science Publications

Keywords

  • Granitoid
  • K-feldspar
  • Nucleation
  • Simple twinning

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