Micro-textures of Hematite in the Liesegang Rocks, Found in Pyrophyllite Deposits, Shobara District, Southwest Japan.

Characteristic micro-textures of hematite found commonly in the Liesegang rocks collected from pyrophyllite ore deposits, Shobara district, southwest Japan were investigated. Detailed observations of the Liesegang rocks under the high magnification reflection microscope with oil immersion lens reveal that almost all of opaque grains are composed of needle-shaped very fine crystals with less than few microns in width and 5-10 microns in length. Moreover, doughnut-like texture, which is characteristic in the Liesegang rock (Yamashita et al., 1996), is mainly composed of the needle-shaped fine crystals. In many cases, the rings are composed of radiated aggregates of the needle-shaped hematite crystals. The size of the most predominant rings is less than 10µm in diameter, and double, triple and multi rings are also common.
The optical properties of these opaque crystals under the reflection microscope are almost similar to those of ordinary hematite, i.e., weak but noticeable bireflectance and distinct anisotropism (e.g., Uytenbogaardt, 1971). X-ray powder diffraction data indicate that most of the opaque minerals are hematite with small amount of goethite. However, under the reflection microscope, distinguishment of the two minerals is not possible.