Structural disparities between chalcedony and macrocrystalline quartz

Examination of length-fast chalcedony by transmission electron microscopy reveals significant structural differences between microcrystalline fibrous quartz and ideal α quartz. Individual crystals that make up chalcedony fibers are elongate along [110] and are twisted about the fiber axis. Streaks in electron diffraction patterns of single fibers indicate pervasive disorder among the {101} and possibly the {011} planes, and in dark-field images the texture of this structural disorder appears dendritic. Because the streak systems associated with {101} and with {011} intersect at the expected locations of primary diffractions associated with the mineral "moganite', demonstrations of the presence of "moganite' require complementary characterization techniques, such as X-ray powder diffraction -from Authors