2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 6
Presentation Time: 2:45 PM


KAWAMURA, Kiichiro, Fukada Geol Institute, 2-13-12, Honkomagome Bunkyo-ku, Tokyo, 113-0021, Japan, OGAWA, Yujiro, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8571, Japan, IKEHARA, Ken, AIST, 1-1-1 Azuma, Tsukuba, 305-8564, Japan and TANIGUCHI, Hidetsugu, Komazawa University Highschool, 1-17-12 Kamiyoga Setagaya-ku, Tokyo, 158-8577, Japan, kichiro@fgi.or.jp

Nucleation and growth of framboidal pyrites are thought to be basically controlled by the bacterial activities. However its process remains unsolved to date. Microscopic and SEM observations of the microtexture of framboidal pyrites suggest the following new growth process. 1) Spherical initial pyrites, nucleated simultaneously, are aggregated to form a framboid of 5-10 micron in size. The spherical pyrites take the euhedral shape during this stage. 2) The framboids precipitate by gravity force (following Stoke's law) to form a geopetal fabric inside the pores of the sediment. Although the framboidal pyrites are suspended by Brownian motion during the stage of small size approximately less than 1 micron, they precipitate as increasing in size by the microcrystal growth. 3) The framboidal pyrites are covered with a membrane composed of phosphorus, probably organic matter. The membrane plays an important role in absorption mechanism of organic matter on the pyrite. The absorption phenomena can be used to remove organic matter from polluted materials. Furthermore the absorption presumably is responsible for formation mechanism of early cell membrane as origin of life. The composition of the membrane and its adsorption mechanism will be further studied.