Mineralogical Study of Rock-alteration to Pottery Stone of Some Pottery Stone Deposits in San-in District

On the mechanism of the Mineralization of Pottery Stone, I

Abstract

The pottery stone called “Tôseki” is not defined mineralogically. And the process of rock-alteration to pottery stone is not studied yet.
In San-in district, there are several localities of pottery stone which may be classified into following three types:
I. Deposits produced by rock-alteration of pitchstone, which intrused into rhyolite-represented by Izushi pottery stone deposit in Hyôgo prefecture.
II. Deposits produced by rock-alteration of quartz porphyry-represented by Tanokouchi pottery stone deposit, Tottori prefecture.
III. Deposits produced by rock-alteration of rhyolite-represented by Amabe pottery stone deposit, Kyôto prefecture.
This paper concerns the geological and mineralogical studies of above three deposits stating in detail on the process of rock-alteration and also the mineralogical significance of pottery stone:
(1) Pottery stone deposits are the products of the replacement and metamorphosis under the influence of epithermal solution rising up along the weak line of mother rock.
During the process of deposition alkalies changed their position; Na₂O being generally leached out because of its smaller molecular volume, while K₂O codeposited with Fe on the circumference of pottery stone due to chemical migration giving lower quality ore so-called “Toraishi”.
(2) Pottery stone, Tôseki, is composed of SiO₂ and Al₂O₃ as chief ingredient, whose analysis is 75-82% SiO₂, 12-16% Al₂O₃, and 1-5% alklies (K₂O+Na₂O). It is white fine ore consisting mainly from quartz, sericite, halloycite and kaolinite, etc.