Hsianghualite (Ca 3 Li 2 [BeSiO 4 ] 3 F 2 , I 2 1 3) is the first new mineral discovered in China in 1958 and is very precious due to its rare occurrence in the Earth. Few studies have reported about hsianghualite during these years. The authors measured the complex morphology of hsianghualite and found a twin structure in hsianghualite crystal by electron backscattered diffraction (EBSD) technique. The pole figures were used to analyze the twin relationship. The twin law of hsianghualite is the twin plane {110}. This twin law is the same as that proposed by crystallographic theoretic analysis in the previous work. EBSD experi- mental study verified our theoretic analysis of the twin structure in the previous work. The twin structure in hsianghualite has never been reported since the discovery of this mineral in 1958.
Non-equilibrium morphology has received much attention from both scientific and engineering points of view for its intricate pattern selection mechanisms and useful industrial application. Most study of non-equilibrium is about the metal, alloy and other simple system. The complex silicate system is rarely involved. However, silicate is very important in geosciences and ceramic industry. In this paper, two kinds of non-equilibrium crystal morphologies of silicate: dendrite of diopside and spherulite of plagioclase, were introduced. Combining with the other kinds of non-equilibrium morphologies, the characteristics of micro-macro and anisotropy-isotropy of the non-equilibrium morphologies were discussed. Dendrite of diopside is micro- and macro-anisotropic, spherulite of plagioclase is micro-anisotropic, but macro-isotropic, fractal of NH4Cl is also micro-anisotropic, but macro-isotropic, dense-branching morphology (DBM) formed in non-crystalline system is micro-and macro-isotropic. Based on the micro-macro interplay on the pattern formation, it is proposed that the interplay between micro-anisotropy of crystal structure vs macro-isotropy of undercooling in crystal growth system will control the morphological evolution. The nucleation rate related to the anisotropy for the morphological evolution was also discussed. The fact that diopside develops dendrite and plagioclase develop spherulite in our experiment is due to their structural anisotropy difference.
