島根・鳥取・岡山・広島県境地域の超塩基性岩に随伴する鉱物(IV) : 島根県広瀬鉱山産アルミニウム透角閃石と岡山県高瀬鉱山産鉄透角閃石

その他

Subtitle : Aluminous Tremolite from the Hirose Mine, Shimane Pref. and Ferrian Tremolite from the Takase Mine, Okayama Pref.
　Abstract: Geology of these area was reported before by the author, so it will not be described on again in this paper.
The sample No. 1 was found at 34 m level of Hirose mine, and the sample No 2 was discovered at new No. 3 level of Takase mine.
Both of the country rock of these samples are pyroxenite composed of enstatite an_d diopside, and a little part of them has been affected by residual magmatic autometamorphism, then tremolite was produced.
It can be considered that the addition of Si0_2 and H_20 to these country rocks (pyroxenite) reacted chemically as the following equation.
3MgSi0_3 (enstatite) +2CaMgSi_20_6 (diopside) +Si0_2 + H_20→ (OH)_2Ca_2Mg_5Si_80_<22> (tremolite) In this reaction, the metamorphism does not advance so as to produce hornblende. The reason why fluorine does not exist in tremolite as shown in the chemical analysis table, is that pyroxenite was not metamorphosed by granitic rock.
On the other hand, harzburgite has been metamorphosed by dioritic rock, and then asbestiform tremolite in small quantities has been crystallized from the harzburgite. The occurrences are sometimes observed in the region The general reaction equation may be expressed as follows.
MgSi0_3 +Mg_2Si0_3 (olivine) +Si0_2 +CaO (from diorite) +H_20 →(OH)_2Ca_2Mg_5Si_80_<22>