Abstract: Dissolution of plagioclase
(andesine) into acidic, neutral and alkaline aqueous solutions
at 20'C and 150'C was studied using batch reactors. Dissolution
under neutral conditions are congruent, whereas, that under acidic
conditions would be incongruent with selective leaching of Al,
Ca and Na, which was estimated from compositions and surface ob-
servation. Dissolution rates (log K [mol feldspar /m2s]) at 25'C
estimated from Si release were -10.93 in H20 (pH 5.8), -9.37 in
0.1N HCI (pH 1.1), -l0.25 in 0.lN HCOOH (pH 2.2), and -9.71 in
0.01N NaOH (pH 12.2) solutions respectively.
Those at 150'C were -7.76 in H20, -7.49 in 0.003N HCl, -6.42 in 0.1N HCl, and -7.76 in 0.01N NaOH. Activation energies were 63.0 kJ/mol in 0.1N HCl, 61.2 kJ/mol in H20, and 37.7 kl/mol in 0.0lN NaOH. The small activation energy under alkaline conditions suggests that the rate controlling process is different from that under neutral and acidic conditions.
*東京学芸大教育地学教室、** 地調地殻熱部、*** 農林水産省国際農林水産業研究センタ−環境資源部
Abstract: This article describes a series of research done on the mineralogy of Canadian soils by the author and his colleagues over the past 35 years. During the period, 1962-77, the research was devoted to the characterization of minerals in soils and sediments with continuing effort to improve analytical methods for mineral identification and characterization. Of the research, a major difference in the clay mineral composition of the western prairie soil and eastern maritime soils was highlighted here. The prairie soils are smectitic, whereas the maritime soils are micaceous. It was noted, however, that potassium available to plants is always sufficient in the prairie soils but not in the maritime soils, although both soils have similar K20 content ( - 3% ). This is obviously reflected in the smectitic composition of the prairie soils. The composition includes smectite and vermiculite component layers as interstratified minerals, all of which can release K relatively easily than illites in the maritime soils as discrete or/and interstratified minerals.
In the following 10 years from 1978-87, the research focused
on various interactions of clay minerals with soil organic matter
and inorganic compounds, as well as on the detection of poorly
crystalline inorganic components in soils. Expandable clay minerals
such as smectite can adsorb water-soluble soil organic matter
between the layers only under low pH conditions, because under
these conditions the majority of soil organic matter molecules
are relatively undissociated and mostly remain neutral. At higher
pH, the molecules dissociate negatively. This illustrates the
importance of pH-dependent charge in the soil system. Oxide, oxyhydroxide,
and hydroxide minerals occurring in soils also possess pH-dependent
charge, thus they react as positively or negatively charged particles
depending upon pH, unlike clay minerals which are permanently
negatively charged. In the soil system, recognizing the presence
of these charges is very important to understand reactions between
minerals, organic matter, metal ions, and agrochemicals. The direction
of research further shifted to make mineralogy interact with other
domains of science in the last I O years. This produced research
work on mineralogy in a microenvironment rhizosphere, mineral
grains as architectural materials for housing soil living habitats
and a mineralogical database of Canadian soils. The role of minerals
in soils is very diverse. Minerals release major and minor elements,
adsorb water, and react with organic and inorganic compounds,
and these actions are environmentally favourable and adverse as
well. Mineral particles of appropriate sizes are apparently effective
for protecting microbes by retarding decomposition of organic
matter. Clay minerals, in particular, provide with large surfaces
to promote reactions and interactions that play an important role
in soil forming processes. Undoubtedly mineralogy will make a
significant contribution to a better understanding of very complicated
soil environments that have a great impact on the well-being of
humankind.
Abstract: Ion thinner is a useful tool for specimen preparation of rock forming minerals for electron microscopy, This paper describes the principle and procedure of ion thinning, and some preparing techniques for ion thinning.
*日本大学文理学部 物理学教室、**新潟大学理学部 地質科学教室