抄録
The Hino diorite mass, intruded into the Paleozoic rocks and Mesozoic volcanic rocks, are exposed within restricted area of western part of Tottori Prefecture.
This dioritic rock is chiefly composed of plagioclase, hornblende, biotite and quartz together with few magnetite, sphane, orthopyroxene and epidote.
In the earlier stage of the weathering, biotite is rapidly altered to secondary minerals such as montmorillonitevermiculite mixed layer mineral, biotite-montmorillonite mixed layer mineral and halloysite. So that, at this stage, the change of chemical composition of biotite differs markedly from that of the fresh rock.
Approaching toward the later stage, biotite is altered to biotite-vermiculite mixed layer mineral and halloysite. But, at this process, the change of chemical composition of biotite is little.
On the other hand, as weathering proceeds, plagioclase and hornblende are gradually elliminated and halloysite appear in stead.
The change of chemical composition of rock in the weathering process is controlled by biotite at earlier stage and by plagioclase at middle stage and by bornblende at later stage.
