Revisiting the Bøggild Intergrowth in Iridescent Labradorite Feldspars: Ordering, Kinetics, and Phase Equilibria

The enigmatic Bøggild intergrowth in iridescent labradorite crystals was revisited light of recent work on the incommensurately modulated structures intermediated plagioclase. Five igneous samples and one metamorphic sample with various compositions lamellar thicknesses were studied this paper. textures characterized conventional transmission electron microscopy (TEM) scanning (STEM). individual lamellae analyzed high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping atom probe tomography (APT). average structure states also compared single-crystal diffraction data (SC-XRD). Na-rich have a composition An44–48, Ca-rich range from An56 to An63. Significant differences between different observed. do not only depend bulk compositions, but thermal history host rock. implications subsolidus phase relationships plagioclase feldspar solid solution are discussed. results cannot be explained by regular symmetrical solvus such as gap, they support an inclined two-phase region that closes at low temperature.