Abstract
Iddingsite occurs as an alteration product of olivine by weathering in the tephras which are widely distributed in South Kanto, Japan.
It is a reddish-brown colored aggregate composed of goethite, lepidochrocite, and hydrous amorphous substance containing silica and magnesia.
It is more abundantly found in the horizon from the base of Musashino (ca. 30, 000-60, 000y.B.P.), to the upper part of Shimosueyoshi (ca. 60, 000-130, 000y.B.P.) tephra layers in Pleistocene.
Regarding iddingsite as the equivalent of olivine, the heavy mineral composition is rather constant from the upper part of Shimosueyoshi tephra layer to the Tachikawa (ca. 10, 000-30, 000y.B.P.) and Musashino tephra layers.
