TrekGEO > Mineral Trail > Koshinetsu region > Fukui pref. > Wollastonite

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Nakatatsu Mine

Kami-Ono, Ono city, Fukui pref., Japan


Width: 50 mm. Wollastonite associated with calcite. The radial groups of white fibers at the top is wollastonite. The surrounding massive white to dark gray parts are aggregate of granular calcite crystals. The dark gray calcite at the bottom exhibits bedding planes, the original sedimentary structure. Note that wollastonite is embossed as it is stronger than calcite to weathering.

Recovered from skarn formed by contact metamorphism of I-type (Magnetite-series) granite. Formed in the Late Triassic (220 Ma).

It is considered that wollastonite was formed by reaction of calcite with the quartz-bearing part such as chert. For example:

3CaCO3 (Calcite) + 3SiO2 (Quartz) = Ca3Si3O9 (Wollastonite) + 3CO2

Wollastonite from this location was described in 1946.


Field of view: 50 mm. The fresh side of the above specimen. The white fibers with a vitreous luster at the top are wollastonite. The white to dark gray parts at the bottom are calcite. The white veins traversing dark gray calcite are also calcite.

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