An interstratified mineral of biotite and vermiculite from the Hase mine, Hitachi-ota city, Ibaragi Prefecture

Abstract

An interstratified mineral of biotite and vermiculite (=hydrobiotite) was found as an alteration mineral of biotite at the Hase mine, Hitachi-ota city, Ibaragi Prefecture. The material used contains vermiculite as an impurity. Chemical composition: Si0₂ 32.78%; TiO₂ 2. 36%; Al₂0₃, 20.38%; Fe₂O₃ 3.96%; FeO 8.58%; Mn0 0.07%; MgO 16.47%; CaO 0.09%; Na₂O 0.29%; K₂O 3.97%; H₂O⁺8.51 %; H₂0^-2.75%; total 100.21%. Although the specimen contains vermiculite, the chemical composition is similar to that of biotite.
The specimen gives a 26.7 Å reflection and its higher orders. The interstratification seems to be produced by a two component stacking of about 60% biotite-like layers and about 40% vermiculite-like layers.