Abstract
The Au-decoration technique of electron microscopy was applied to the crystal surfaces of pyrophyllite collected from the Urals, Russia. The modes of occurrence of pyrophyllite ores in the Urals are briefly divided into four types, such as the alteration zone of iron sulfide ore deposit, veins with the gold deposit, sediment with coal layers, and weathering crust. Pyrophyllite occurs mainly in the hydrothermal alteration zones of the iron sulfide deposits. In this study, pyrophyllite specimens were collected from the three iron sulfide deposits, i.e., Gay, Kur-Yurt-Tau and Chistogor deposits.
The specimens investigated exclusively exhibited growth patterns of parallel steps with varying step separations. In generally circular and polygonal spiral growth patterns are observed on the crystal surfaces of illite, kaolinite and chlorite formed under the hydrothermal alteration. It is considered from the difference of these morphological characteristics on the crystal surfaces that pyrophyllite particles were formed under the higher temperature and/or supersaturation comparing with other hydrothermal clay minerals.
