Here’s an unusual rock that represents a cavity-filling in a pegmatitic syenite. The syenite host rock is dominated by large, whitish albite crystals (= sodium plagioclase feldspar, NaAlSi3O8) (see left & right edges of photo). The cavity fill has nice, large, bluish sodalite crystals (= sodium chloro-aluminosilicate, Na8(AlSiO4)6Cl2)). Surrounding each sodalite is a radiating spray of very dark green needles of aegirine pyroxene (= sodium iron silicate, NaFeSi2O6).
The rock comes from southeastern British Columbia’s Ice River Complex. The Ice River is an 18-kilometer long, 29-square kilometer, backward J-shaped alkaline igneous intrusion emplaced in Cambro-Ordovician passive-margin limestones and shales.
Age: ~356 million years (Tournaisian Stage, Early Mississippian or Famennian Stage, Upper Devonian, depending on which geologic time scale one uses)
Sodalite-aegirine-albite pegmatite (field of view ~7.1 cm across) from the Ice River Complex of British Columbia, Canada.
Blue = sodalite
Very dark green = aegirine pyroxene
Whitish = albite/sodium plagioclase feldspar
Rock info. from Tony Peterson.