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Shoushi-gan ( 松脂岩 )

Shoushi-gan ( 松脂岩 ) in Japan

There is a stone called Shoushi-gan ( 松脂岩 ) in Japan.

It is prefectural stone of Aich prefecture located in the Chubu region which is a region in the middle of Honshu, Japan's main island.

"Shoushi" means pine-resin and "-gan" means rock in Japanese.

Shoushi-gan is a dull black glassy volcanic rock.

Shoushi-gan ( 松脂岩 ) Pitchstone

It is similar to obsidian but is defined by the International Union of Geological Sciences as having a higher water content.

Obsidian contains water less than 1% but Shoushi-gan contains water about 1% to 10%.

Now you might take notice of something.

Yes, Shoushi-gan is Pitchstone.

Shoushi-gan ( 松脂岩 ) Pitchstone

Pitchstone has an irregular hackly fracture not a conchoidal fracture. That is due to its coarser (than obsidian) crystal structure.

By the way, Pitchstone(Shoushi-gan) is categorized in Igneous rock which is one of the three main rock types, the others being Sedimentary and Metamorphic.

In terms of modes of occurrence, igneous rocks can be either intrusive (plutonic and hypabyssal) or extrusive (volcanic).

And for Volcanic rock, it can be classified according to silica content as follows:

  • >69 % SiO2:rhyolite
  • 63-69% SiO2:dacite
  • 52-63% SiO2:andesite
  • 45-52% SiO2:basalt
  • < 45% SiO2:komatiite

Pitchstone(Shoushi-gan) is kind of distinctive rhyolite.

Shoushi-gan(Pitchstone) has an unique feature as smooth and glistening surface as rosin.

The feature is something special and I like it.

Shoushi-gan ( 松脂岩 ) Pitchstone

Shoushi-gan ( 松脂岩 ) Pitchstone

Shoushi-gan ( 松脂岩 ) Pitchstone

As Shoushi-gan is registered as prefectural stone of Aich prefecture, Shoushi-gan is mined in Shinshiro (新城市) which is a city located in east-central Aichi Prefecture.

In Shinshiro, from Houraiji Mountain (鳳来寺山) through Tanamachi (棚町), Shoushi-gan is mined.

Especially, Kagami-iwa of Houraiji Mountain (鳳来寺山の鏡岩) is well-known.

Kagami-iwa could be regarded as a symbol of Houraiji Mountain.

It is wall of Shoushi-gan and its size is about 70m height and 250m width.