Sukune Takenouchi

Stability of pentlandite in the Fe-Ni-Co-S system

Pentlandite has a wide compositional range in the Fe-Ni-Co-S system and the Fe-Ni-S system. The metal : sulfur atomic ratio is approximately 9 : 8. The Co content of pentlandite from the Kamaishi ore deposit and one from the Outokumpu ore deposit (Knop et al. 1965) varies from a Co-free to nearly a Co9S8 composition. Pentlandite forms a complete solid solution between (Fe, Ni)9±xS8 and Co9±xS8 in the 600°–300°C temperature range. On the other hand, it is presumed that the pentlandite solid solution decomposes into two fields toward the (Fe, Ni)9S8 and Co9S8 members at 200°C. The field of solid solution at 500°C is the most extensive and includes all of the other solid-solution fields. The metal : sulfur ratio of the solid solution varies systematically, i.e., the Fe-rich field sinks toward the Fe-Ni-Co plane away from the M9S8 section, and contrarily the Ni-rich field shifts toward the sulfur apex. The d044 value decreases with increasing S, Ni, or Co contents in pentlandite. The Kamaishi pentlandites, Iwate Prefecture, Japan, lie within or close to the solid-solution field at 300°C, showing a very good correlation with the Co : Ni ratio of the homogeneous natural pyrrhotite phase.

Hydraulic Fracturing in Geological Processes: A Review

In the Earth’s crust there occur many emplacement bodies and fissure-filling columns, such as salt plugs, igneous stocks, sheet intrusions, clastic dikes, and mineral veins. Since they were formed with relation to the activity of some fluid materials, such as plastic salt, magma, water, aqueous solution, they may be analogs of hydraulic fractures. With the increase of pore-pressure, rocks become weak and also brittle even under a relatively high confining pressure. This implies that the pore-pressure affects the fracture pattern as well as the strength of rocks.