Bytownite
Toyosaka, Matsushiro village, Nagano city, Nagano pref., Japan
IMA approved name
Anorthite var. bytownite
Width of crystals: 10 mm. Dispatched bytownite. Some bytownite crystals are red. The red color was explained by copper inclusions on anorthite crystals at other localities but this specimen has not been confirmed.
The formation process of red anorthite including copper is explained as follows: Anorthite formed at high temperature may include metal elements such as Cu and Zn.
(1-x)CaAl2Si2O8 + xH3(Cu,Zn)Si3O8, where x << 1
Cu and Zn end members become unstable at lower tempeature, and Cu and Zn are formed as exolution lamellae.
4H3(Cu,Zn)Si3O8 = 4(Cu,Zn) + 3(SiO2)4 + 6H2O + O2
Recovered from weathered basaltic tuff. Formed in the early Miocene (16 Ma).
Bytownite from this location was described in 1994.