Abstract:

Chemical etching with 20% HF (HF+distilled water, volume rate) at room temperature was studied on seven sections
of olivine crystals, i.e., parallel twin (100), (010), (001), rhombic prism (110), (011), (101) and rhombic dipyramid (111) sections.
AFM (Atomic Force Microscopy) and DIC (Differential Interference Contrast Microscope) methods were used to analyze these
etched sections . With a fixed shape and angle, etch figures were different in each case, but all are elongated to [010] and
shortened to [100]. The face indices and the crystallographic orientation of a single crystal were only determined by the specific
etch figures, also in rocks. Meanwhile, the etch figure symmetry displayed the point group mmm of olivine. Measured by a
specific shape in DIC 200×, the reaction rate of the seven sections was v (010)>v (110)>v (100)>v (111)>v (101)>v (001)>v (011). Classified the
etched random grain section indices identified by typical etch figure, the crystallographic preferred orientation of olivine grains in
peridotites from Bixiling in Dabieshan areas, was defined as having strong maxima of [100]， subnormal to the foliation， and strong
maxima of [010]， subparallel to the lineation. These observations may suggest that specific tectonic events affected the peridotites
at the localities.

Key words: Olivine；Etch Pits；Crystallographic Orientation, Petrofabrics