Study of sphalerite from Hosokura mine by electron microscope

Abstract

Thin films (110) of fibrous sphalerite from Hosokura mine were examined under the electron microscope.
It was found out that an axis of fibrous sphalerite is parallel to _??_111_??_ and that many polysynthetic twins occur at righ angles to the _??_111_??_ axis. Because of the occurrence of these polysynthetic twins, the cleavage plane (110) was observed to occur parallel to the axis.
Many hexagonal and trigonal growth patterns were observed on the (111) plane of the crystals. This indicates that this fibrous sphalerite from Hosokura mine originally developed as a parallel intergrowth of fibrous fine-twinned sphalerite and wurtzite since it is generally known that crystals of ZnS showing hexagonal growth pattern grow as wurtzite and those that show trigonal pattern grow as sphalerite. X-ray diffraction pattern and electron diffraction pattern, however, did not show the presence of wurtzite in the specimen. It may be supposed, therefore, that the original wurtzite was transformed to sphalerite through geologic age.
The massive and fibrous sphalerite samples were heated in a vacuum silica tube, and were observed under electron microscope. The reaction trend of the thermal transition is as follows.
Cubic packing (%) 100 100>
Reaction trend sphalerite → polysynthetic twinned sphalerite→
66.6 50 50> 0<
→6H, 4H polytype → complex polytype → wurtzite
In thin films of heated specimen, many fine streaks of complex poly-types, twins of sphalerite and stacking faults were found.
The fibrous sphalerite with many twins was thought to be premonitory condition for the phase transition. The c_??_0001_??_ axis of wurtzite formed from fibrous sphalerite coincide with the _??_111_??_ axis parallel to the elongation of fiber.