Foid Syenite Hand Sample
Foid Syenite Thin Section

Foid Syenite

IUGS Definition ( QAPF Chart ) ( FAP Chart )

Foid Syenite: "A collective term for leucocratic alkaline plutonic rocks consisting of feldspathoids (10%-60% of the felsic minerals), alkali feldspar and mafic minerals."
Photos
Typical Minerals
  • alkali feldspar: perthitic orthoclase and microcline
  • plagioclase feldspar (often as perthitic components)
  • feldspathoid minerals
  • biotite
  • hornblende
  • clinopyroxene: diopside, augite
  • accessory minerals: sphene, apatite, zircon, opaque oxides, olivine