Sillimanite
Nekoyama mine
Nagano, Manno city, Nakatado county, Kagawa pref., Japan
Field of view: 2 mm. A group of sillimanite. The columnar group of white fibers is sillimanite.
Recovered from a pyrophyllite deposit formed by pyrophyllitization alteration of granite and associated hornfels in a low-pressure regional metamorphic belt by andesite. Formed in the middle Miocene (13 Ma).
Sillimanite from this location was described in 1934, and was designated the prefectural mineral of Kagawa in 2016 by the Geological Society of Japan.
Other localities
- Nekoyama (Pyrophyllitization, Fibrous)
- Mount Asama (Sanidinite facies, Fibrous)