ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Dendritic cordierite occurs in argillaceous hornfels from the Toki area, Gifu Prefecture, Japan. The cordierite crystal consists of ‘c-arms’ elongated parallel to the c-axes and ‘a-arms’ perpendicular to the c-axis. The latter arms could be divided into six kinds of untwinned ‘a-arms’ with different growth directions elongated parallel to the respective a-axis and twinned ‘a-arms’ elongated parallel to the (110) twin plane. ‘A-arms’ branch out from ‘c-arms’ or other ‘a-arms’ with different growth directions and ‘c-arms’ sometimes branch out from a-arms, leading to a tree-like structure. Each of the ‘c-arms’ contains three kinds of domains related by a three-fold axis about the c-axis. These domains are irregularly distributed without any relation to the shape of the ‘c-arm’ and the domain boundaries are of zigzag shape. This domain arrangement suggests that ‘c-arms’ grew as hexagonal cordierite and were later transformed into orthorhombic cordierite. The fact that each untwinned ‘a-arm’ has a fixed growth direction to its orientation suggests that the ‘a-arms’ grew as an orthorhombic cordierite. From the growth directions of ‘c-’ and ‘a-arms’, orthorhombic and hexagonal phases are considered to grow preferentially along the c- and a-axes, respectively. The branching of a new arm is explained by nucleation on an old arm with a different preferred growth direction. The preferential growth is discussed in terms of a significant chemical potential gradient of the cordierite component. This has been preserved in the mineral zoning observed in the matrix around the cordierite porphyroblast.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01575617
