Abstract
Herschelite, defined as a Na-rich zeolite with the chabazite structure, has been studied with optical and scanning electron microscopy, X-ray powder diffraction, and electronmicroprobe microprobea analysis. Herschelite consists of a combination of {1010}, {0001}, and {1011} forms, showing hexagonal symmetry 6/mmm. The three corresponding sectors show different textures between crossed polarizers, though they are chemically homogeneous. The (1010) face consists of fine striations normal to the c axis, and the corresponding sector shows fine polysynthetic twins normal to the c axis. The (0001) face is covered by small chabazite crystals with three rhombic {1011} faces that are related by twofold rotation twins, and the {0001} sector shows a fibrous texture normal to the (0001) face. Some herschelitec rystalss how a biconvex lens-like form, whose surfaces consist of fine chabazite crystals with three rhombic {1011} faces. Thin sections show a fibrous texture that corresponds to the fine crystals on the surface. Some herschelite crystals have a gmelinite rim whose (0001) surface consists of a spiral growth pattern. Herschelite consists of triclinic sectors with fine-scale twinning, and single herschelite crystals do not occur.
