THE OCCURRENCE AND STRUCTURE OF VERMIFORM CHLORITE

Abstract

To understand the origin of its unique morphology, the structure of vermiform chlorite has been investigated. Two chlorite specimens (magnesian chamosite) were analyzed: vermicular aggregates in quartz-feldspar veins in a pelitic schist, and those grown on a quartz single-crystal surface. Both specimens show very similar textures; they are composed of pseudohexagonal chlorite plates of several tens μm in lateral size and several hundreds nm in packet thickness, stacked to form long vermicular aggregates up to several hundreds μm. Chemical analyses indicated that the two specimens have similar compositions with ^<IV>Al 1.2〜1.3 per 4.0 sites and Fe/(Mg+Fe) ratio of 〜0.55. XRD and EBSD indicate IIbb semi-random stacking. HRTEM shows that the stacking is considerably disordered in terms both of the layer orientation and direction of the interlayer displacement. The vermicular morphology of chlorite is probably originated from a relatively faster spiral growth along the stacking in hydrothermal fluid.