Glauconites in the recent marine sediment off the coast of Nomo Peninsula and Paleogene Saburaishi formation, Nagasaki Prefecture

Abstract

Two kinds of glauconite grains, one (G-A) in the recent marine sediment off the coast of Nomo Peninsula and the other (G-B) in the Paleogene Saburaishi formation, have been investigated by means of x-ray diffraction method, differential thermal analysis and chemical analysis. Both glauconite grains have been found to consist essentially of randomly interstratified mica and montmorillonite; these minerals are glauconite sensu lato. G-A contains from 45 to 85 per cent montmorillonite layers and its fine grain part is rather rich in montmorillonite layers. G-B also contains 20 per cent montmorillonite layers. Chemical formulae of the glauconites are as follows:
G-A-2 (50 per cent montmorillonite layers)
(K_0.41Na_0.171/2Ca_0.02) _0.60 (Fe³⁺_0.93Al_0.59Mg_0.58Fe²⁺_0.07) _2.17 (Si_3.55Al_0.45) _4.00O₁₀ (OH) ₂
G-B (20 per cent montmorillonite layers)
K_0.59Na_0.271/2Ca_{0.02 0.88} (Al_0.86Fe³⁺_0.76Mg_0.30Fe²⁺_0.08) _2.00 (Si_3.50Al_0.50) _4.00O₁₀ (OH) ₂
In relation to the degree of crystallinity, proportion of montmorillonite layers, microscopictexture and associated minerals, the genesis of glauconite has been discussed.