Texture of lutecite

Lutecite is an aggregate of microcrystalline silica; its variety with a hexagon form is known as hexalite. Textures of lutecite and hexalite from the Arz-Bord Range, in northwestern Gobi, Mongolia, and from Banyan-obo, China, were observed by optical microscopy, synchrotron X-ray diffraction, and transmission electron microscopy (TEM). Cross sections of lutecite and hexalite observed through optical microscopy show fibrous textures. TEM observations revealed that the quartz crystals constituting each fiber exhibit irregular shapes elongated parallel to [212], which is nearly perpendicular to (101̄); a width of 0.5 urn; and length of a few micrometers. The results of selected area electron diffraction analyses show that the fiber bundles have V-shaped cross textures, and the crystals are twinned according to the Reichenstein-Grieserntal law. X-ray diffraction analysis indicates a total moganite content of approximately 10 wt% in this lutecite aggregate, and moganite appears as irregular-shaped domains within quartz under high-resolution TEM.