The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists

Show abstractHide 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.

View full abstract

Download PDF (3500K)

The Happo-O'ne ultrabasic rock mass is situated in the north-eastern part of the Hida marginal structural belt and composed mainly of dunite or serpentinized dunite.
Olivine with well-developed cleavage, which is so resemble to the “cleavable olivine” reported from northern California (Hawkes, 1946) and Komori (Kuorda and Shimoda, 1967), is discovered in the dunite of this area. The dunite containing the cleavable olivine is found in the core of the rock mass as a relict and surrounded with strongly sheared dunite. The petrographical and petrochemical characters of this rock mass are presented, and furthermore, some properties of the cleavable olivine are inspected.

View full abstract

Register with J-STAGE for free!