Bunji Iwasaki

High‐Pressure Synthesis of the Stoichiometric Compound FeO

A stoichiometric compound, Fe1.000O, was synthesized at high pressures above 36 kbar at 770°C by a reaction between Fe0.950O and metallic iron. The cell dimension of Fe1.000O was determined to be 4.323±0.001 A at atmosphere pressure.

Nature of volcanic gases and volcanic eruption

4. Conclusion1) The chemical composition of volcanic gases emitted from fumaroles and hot springs represents their stages of the differentiation of magmatic emanation at their effusing points, although the nature of volcanic gases varies with their orifice temperatures and geological environments. Consequently, changes of the chemical composition of volcanic gases indicate the variations in volcanic activities or geological environments.As we have seen in Table 1, halogen compounds and sulfur dioxide represent the earlier stage of the differentiation of magmatic emanation. Then the ratios such as F/CO2, Cl/CO2, Cl/SO2, SO2/CO2, SO2/H2S, H2S/CO2 and CO2/N2 may be used for the detection of the leakage of magmatic emanation depending on their stage of the differentiation of magmatic emanation and their geological environments. Laboratory experiment on heat treatment of igneous rocks supported the tendency of differentiation of volcanic gases obtained from the observation of natural volcanic gases.2) Periodic variations of discharges, temperatures, and chemical compositions of volcanic gases from geysers have been fully observed over the total eruption period of geyser action. By these studies and model experiments, the time and nature of eruptions of geysers could be satisfactorily predicted.3) Radioactivity of the volcanic gases and Tn/Rn can also be used effectively for this purpose, particularly this ratio of two isotopes is very useful for the study of transportation phenomena because the half-lives of each isotope are quite different from each other.

Differentation of magmatic emanation

Chemical properties of magmatic emanation can be estimated roughly by i) volatiles from rocks by heating at various temperatures, ii) volcanic emanations, iii) residual magmatic emanations, iv) calculation from chemical equilibrium between volatile matters and magmas. Magmatic emanation is assumed to consist all of the volatile matters in magmas such asH2O, HCl, HF, SO2H2S, H2,CO 2,N2 and others (halides, etc.) at about 1200°C, although various kinds of magmatic emanations can be formed at different conditions. Magmatic emanation separated from magmas will change their chemical properties by many factors such as changes of temperature and pressure (displacement of chemical equilibrium), and reactions with other substances and it will differentiate into volcanic gases, volcanic waters, volcanic sublimates, and hydrothermal deposits (hot spring deposits).At temperatures above the critical point of water, separation of solid phase (sublimates), liquid phase, and displacement of chemical equilibrium may take place, and gaseous phase will gradually change their chemical properties as will be seen at many fumaroles. Chloride, hydrogen, andSO2 contents will gradually decrease along with lowering temperature.Once aqueous liquid phase appears below the critical point of water, all the soluble materials may dissolve into this hydrothermal solution. Consequently, the gaseous phase at this stage must have usually a little hydrogen chloride as is observed at many fumaroles. Aqueous solutions must be of acidic nature by dissolution of acid forming components, and by hydrolysis (Chloride type). When a self-reduction-oxidation reaction of sulfurous acid takes place, an aqueous solution of sulfate type will be formed. At this stage, solid phases consist of the remained sublimates which are difficultly soluble in aqueous solution, and deposits formed by reaction in the hydrothermal solutions.The gaseous phases below the boiling point of water, have usually a little water, and consist mainly ofCO2 type,H2S type,N2 type, and mixed type owing to elimination or addition of components by reactions with waters or wall rocks according to their geological conditions. Aqueous solutions which was of acidic nature must be changed into alkaline solutions by reaction with wall rocks for a long time. When the oxidation of sulfur compounds takes place, an aqueous solution of sulfate type will be formed. Hydrogen sulfide type of water will be formed by reaction of sulfides with acid waters or absorption of hydrogen sulfide. Carbonate type of water will be formed whenCO2 is absorbed. Solid phases at this stage consist usually of hydrothermal deposits except for that at solfatara or mofette.The course of differentiation of magmatic emanation could take place in more complicated ways than that of magmatic differentiation.