Fayalite aggregate is a rootless rock black in color and consists almost exclusively of fayalite一(Mg0.0169 Fe0.9802Mn0.003)2 [SiO4].The crystals are tabular and columnar in form with the largest grain size reaching 10 mm. The aggregate shows over-cooling texture `with dendrite, In this paper, systematically mineralogic data are given about this rare fayalite whose composition approaches the erid and member component of fayalite.