Oriented growth of chlorite and zoisite in plagioclase as alteration products –examples of graphoepitaxy–

Abstract

Chlorite and zoisite were observed as alteration products in a plagioclase from the archean anorthosite complex, Ontario, Canada. They were often grown as layers along cleavages of the host plagioclase. The orientation relations between alteration products and host plagioclase were determined using X-ray diffraction. C^*_chlorite was parallel to c^*_plagioclase. There are many chlorite grains where a- and b-axes of chlorite grains show no crystallographically significant orientation in (001) of plagioclase with keeping c^*_chlorite//c^*_plagioclase, A^*_zoisite was nearly parallel to c^*_plagioclase and b_zoisite was parallel to a_plagiociase. However, no lattice matchings were found between host plagioclase and the alteration products. It can be concluded that chlorite and zoisite grew on the surface of (001) cleavage of plagioclase according to the graphoepitaxy process.