Abstract
The Oshima-Tôbetsu district here mentioned is situated in the southern part of the Oshima Peninsula in Hokkaido. In this paper, the twin types and the relation between zoning and twinning in plagioclases from hornfels are described. The hornfelses were collected from contacts between rhyolite dykes and tuffaceous mudstone belonging to the Mohejigawa formation in Neogene Tertiary age. The rock is fine-grained, compact, massive and black in colour with blastopsammitic texture in thin-sections. The essential minerals are granular plagioclase, quartz, glass, biotite, hornblende, hypersthene, magnetite with accessory chlorite and sericite. The plagioclases (An43) are mainly composed of untwinned grains with a small amount of twinned crystals. Most of the twinning show pericline and albite laws, while Carlsbad and albite-Carlsbad laws are rarely present. Lastly, the writer presents some considerations on the genetic aspects of C-twin in plagioclases according to Gorai (1951).
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
