Date unknown / Otome mine (Yamanashi) / Wakabayashi collection, Department of Mineralogy, UMUT

Two separate crystals of the same kind which developed attached to each other with a crystallographically significant orientation relation are called twins. Among quartz many kinds of twins are known and the type of the present specimen, characterized by its V-like form, is called “Japanese Twin.” The angle between the two crystals is 84o34’. This type of twin is often observed in quartz specimens from the Otome mine (Yamanashi Pref.). Quartz usually shows a hexagonal prism form but the Japanese twin shows a hexagonal plate form, the reason of which is not clarified yet.

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