The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists

Some parts of the ultramafic bodies in the Kitakami mountainland have been metamorphosed by the granitic intrusions. The forsterite, which is presumably a metamorphic mineral, in the ultramafic rock metamorphosed by the Hitokabe granitic body at Daito-machi, Iwate Prefecture, has been studied. The chemical formula of the forsterite is determined as (Mg_1.87 Fe²⁺_0.11 Fe³⁺_0.01 Ni_0.11)_2.00 Si_1.00 O_4.00. Chemically no difference is observed between this forsterite and the forsterite in the ordinary ultramafic rocks. Some consideration of the chemical similarity of the two types of olivines is discussed. This forsterite is probably regenerated together with talc by thermal metamorphism of a serpentine at the P-T condition corresponding to the hornblende hornfels facies.

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Experimental petrology is defined here as a branch of petrology mainly based on the high temperature and pressure experiments on silicate systems in order to elucidate the genesis of various kinds of rocks. The development of experimental petrology can be divided into the following three stages.
The first stage, from 1850 to 1906, is represented by synthetic works on many minerals and rocks, mainly by the French schools, and also by other European scientists. No reliable quantitative data were obtained, and their experiments were not reproducible.
The second stage, from 1907 to 1949, began with the establishment of the Geophysical Laboratory of Carnegie Institution of Washington in June, 1907. Through numerous quantitative researches on the important anhydrous silicate systems from the physico-chemical view point, the Laboratory has made the greatest contribution to the understanding of the genesis of igneous and metamorphic rocks. Especially N. L. Bowen of this Laboratory proposed a new hypothesis, “Reaction Principle in petrogenesis”, which has served as a guiding principle in petrology during the twenties and thirties of this century.
The third stage is characterized by the high pressure researches which have become possible through the development of the high pressure physics during and after the World War II. Pressures up to 10⁵ atmosphere and temperatures up to 1, 500°C can be attained without too much difficulties. Systems containing more than one volatile component have also been studied. Thus it is now possible to produce the conditions of the mantle about several hundreds of kilometers below the earth's surface in the laboratories, and to discuss quantitatively the genesis of magmas, igneous and metamorphic rocks under extremely high pressure.

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