A STUDY OF THE TEXTURE OF CHERT IN KUZUU AREA, TOCHIGI PREFECTURE, JAPAN

Abstract

The Permian and Triassic strata of the Kuzuu area are composed of chert, sandstone, shale and limestone. Chert accounts for 40 per cent of a thick sequence of the strata. Most of the chert are well thin-bedded, and minor portions are ill-bedded and massive. They are various in colors, but are predominantly gray. Under the microscope, textures of quartz in chert may be divided into three forms: microgranular, snow flake and radially fibrous. Snow flake quartz is a aggregate of grains with irregular and indistinct boundaries, and ranges in size from 10 to 30 microns. Bedded chert consists of three forms of quartz, while massive chert consists mostly of microgranular quartz. Electron microscopic observations show that fracture surfaces of chert have three types: novaculite, intermediate and spongy. Comparing the observations of the polarizing and electron microscopes, microgranular texture corresponds to novaculite type. Snow flake and radially fibrous quartz are indistinguishable from each other under the electron microscope, and both show chiefly intermediate type and partly spongy type surfaces. Remains of radiolaria and sponge spicules are composed commonly of clusters of snow flake quartz as well as radially fibrous quartz. Microgranular and snow flake quartz are probably derived from both organic and inorganic silica.