新潟県魚沼層群 SK030 火山灰層中のジルコン双晶：形態，累帯構造，内部構造

Twin crystals of zircon in SK030 volcanic ash layer in Uonuma Formation, which is Cenozoic strata in Niigata Prefecture, central Japan, were examined mineralogically. Zircon in the SK030 layer was along with monazite, xenotime and corundum crystals. Major twin types were contact twin and penetration twin. Based on the twin forms, the former is subdivided into Fantype I and II, and the latter into Wedgetype I and II. Cathod luminescence (CL) images of the zircon twins showed growth layer. In zircon crystals with the penetration twin, complex growth patterns were observed. Base do n high resolution transmission electron micorscopic images and reciprocal lattice analysis of the corresponding ED patterns of the twin structure, the twin plane was determined as {112} plane.