In the Quarry at Oya, Utsunomiya City, Tochigi Prefecture, Japan

Ind. Health, 1972, 10, 24.

OXYGEN CONSUMPTION OF CLAY MINERALS IN THE QUARRY AT OYA, UTSUNOMIYA CITY, TOCHIGI PREFECTURE, JAPAN

Norihiko KOHYAMA and Hisato HAYASHI

Tokyo University of Education, Otsuka, Bunkyo-ku, Tokyo

and National Institute of Industrial Health, Kizuki-Sumiyoshi, Nakahara-ku, Kawasaki

(Received June 30, 1972)

The tuffaceous sediments are widely distributed in Japan, and have utilized for building stone at every where for many centuries. The production of the tuffaceous sediments at Oya, Tochigi Prefecture, is regarded as the largest in Japan. This tuffaceous sediment called Oya-ishi, contains many altered volcanic rock fragments. We have experienced that there are only 19% of oxygen in the air at some level of quarries where exposed large amount of altered materials in tuffaceous sediments. The accidents due to oxygen deficiency have happened and will be happened where the worksite is narrow and ill-ventilation, especially in places where are absorbent and/or dilution agents of oxygen. We found that the strong absorbent in the quarry is the altered volcanic material called Miso. The Miso is confirmed the mixture of ferrous dioctahedral and ferrous trioctahedral smectite which are situated in deep portions of the quarry, and are stable under the reducing environment. The Miso is commonly dark blue in colour in unweathered deep places, but easily turns to black within a few hour and finally to brown in a few weeks. The oxidized Miso is recognized as the mixture of ferric dioctahedral and ferric trioctahedral smectite without any other impurities such as iron oxides. The ferrous smectites being stable under the reducing condition, absorb oxygen to become the stable ferric smectites under the normal condition, and oxygen is consumed by this reaction. It may be a first report that ferrous iron in the structure of minerals is so easily and spontaneously oxidized to ferric iron in them under the normal temperature and

environment.

Recently many accidents due to oxygen deficiency have occurred in various kinds of industries in Japan. The construction industry has the largest number of this kind of accidents, followed by the mining, the clearing, the chemical and food industries, in descending order. However the accidents in both the construction industry and mining occupied one thirds of them. The accidents due to oxygen deficiency happen where the worksite is narrow and has ill-ventilation, especially in place where there are absorbent and/or dilution agents of oxygen. In the course of our investigation on the causes of oxygen

24 OXYGEN CONSUMPTION OF CLAY MINERALS deficiency in underground works, we found that the iron-rich smectite, a kind of clay minerals, in tuffaceous sediments at Oya, Tochigi Prefecture is a strong absorbent of oxygen. The production of tuffaceous sediments at Oya is regaded as the largest in Japan. With development of quarrying thechniques, the shafts are dug deep, and the drifts are excavated complicately through tuffaceous sediments. In consequence, the worksite have a tendency to be narrow and ill-ventilation.

This paper describes the mineralogical characteristics of the iron-rich smectites in the quarry at Oya, and the mechanism of oxygen consumption.

DESCRIPTION OF ROCK INDUSTRY

Neogene system is distributed wider than those of any other period, and con- sists of large amounts of volcanic materials and pyroclastics. Since the rocks are green in colour, they have been customarily called "Green tuff". The rocks called green tuff having been deposited in Miocene epoch are extensively distributed in southwestern part of Hokkaido, the Inner zone and Fossa Magna Region in Honshu Island. These regions are called "Green tuff region". These rocks have utilized for building stone at everywhere in this region. There are about 300 places of production for tuffaceous sediments in Japan. The famous places of the production are located in green tuff region and shown in Fig. 1. Oya-ishi is one of the principal building stone and its production is the largest

Fig. 1. Distribution of Neogen system and famous places of quarries. Note; A: Neogen System B: Places of Quarry

25 N. KOHYAMA AND H. HAYASHI in Japan. It has produced in Oya district, Utsunomiya City, Tochigi Prefecture. The pumice tuff in this district contains many volcanic rock fragments with a mean diameter of a few cm, and commonly angular shape. The getting and dres- sing of the tuff has been a main industry in this district for many centuries. Oya-ishi is in general use as the materials of the building and engineering such as warehouse, workshop, fire place, kiln, stone wall and foundation stone, because they are cheap and readily taken to dig and manufacture. A small amount of Oyai-shi are used as the materials of sculpture. In Oya district, the quarries and pits are made in hills and the lowland where is along the hills, and prospected and excavated recently. The output of the pumice tuff in Oya district from 1912 to 1971 is given in Fig. 2. In 1947 the total production of Oya-ishi was reported to be about 200,000 tons. The production started to rise steeply since 1956, because quarrying auto-machines such as chain saw have come into use in every quarry in this district. Although the production of Oya-ishi totalled 780,000 tons in 1970, the quarries tend to dig vertically and horizontally in the underground, and depth of the quarries attains to 110 m from the surface of the earth. Openpit or crosscut- ting was once main method for getting of Oya-ishi in hillsite, but recently most of quarries consist of a vertical shaft with workings of the room and pillar methods. As a result, many accidents such as depressions, rockfallings and collapses have ocurred in this district, because many enlarged caves have remained in underground. A few accidents have happened in every year during past 2 decades.

Fig. 2. The production of Oya-ishi from 1912 to 1971.

There are 155 quarries in Oya district at present, but many are small concerns of the family type. The locations of most of quarries are indicated in Fig. 3.

STRATIGRAPHIC SEQUENCE AND DESCRIPTION OF ROCK

Ova-ishi being glassy tuff is exposed in the district of about 6.8 km2, situated about 8 km northwest of Utsunomiya City, Tochigi Prefecture. It is coarse-grained,

26 OXYGEN CONSUMPTION OF CLAY MINERALS

Fig. 3. The locations of the quarries at Oya district, Tochigi Prefecture. Closed circles indicate quarries.

porous, massive and largely composed of pumice fragments. Oya-ishi occurs as thick beds about 300 m in total thickness. In places, round or elliptical bodies of 50 cm maximun diameter and consisting of minute rhyolitic glass fragments, are scattered through the rocks. These round or elliptical bodies have been perfectly altered to clay minerals, the iron-rich smectites. These altered volcanic materials are called "Miso", and the stratum consisting large amount of altered volcanic

Fig. 4. The arrengement of the altered materials called Miso in tuffaceous sediments at Oya, Tochigi Prefecture.

27 N. KOHYAMA AND H. HAYASHI materials, Miso, is called "Tohri". The stratum concentrating with the altered fragments, Miso, alternates generally in parallel with a zone of no altered fragments. The arrengement of Miso in tuffaceous sediments is shown in Fig. 4. Many strata of Tohri are intercalated in Oya-ishi, and dip monoclinally about 10•‹ to northeast or east. The thickness of these strata is variable from 1 m to 30 m. The tuffaceous sediments in Oya district can be devided into three formations such as upper, middle and lower formation by strata of Tohri. Oya-ishi has been gotten mainly from the middle formation and the upper formation of the Oya tuffaceous sediments. The lower formation is easily decomposed by weathering, so it has no value as building stone. The alternation of sandstone and shale are intercalated between the lower and the middle formation. The middle formation is also devided, in ascending order, into lower, middle and upper member by the situation of Tohri.

The lower member of this formation has no value for the building stone, because it contains frequently silicified rock fragments such as rhyolite and glassy rock etc.. The middle and upper member in the middle formation are quarried mainly for the building stone. The upper formation distributing eastern part of this district, is classified into two members such as upper and lower member. The lower member has the best quality of the building stone, but the upper member

Table 1. Generalized section and characteristics of sedimentary rocks in Oya district.

28 OXYGEN CONSUMPTION OF CLAY MINERALS has no value for building stone, because it contains large amount of Miso being 20-30cm in size. Stratigraphic sequence and characteristics of rocks, according to Ota1.2), is summerized in Table 1. Relationship between facies of Oya-ishi and the depth of quarries in representa- tive area is in Fig. 5. Since the strike of Oya-ishi is N-S direction, the quarries distributed in north-to-south trend are getting Oya-ishi from same horizon of the Oya tuffaceous sediments. As shown in Table 2, most of production of western area has come from the middle member of the middle formation. Oya-ishi occurred in central area has been excavated from the upper member of the middle forma-

Fig. 5. Relationship between facies of Oya-ishi and the depth of quarries in Oya district. Note; Black space: cross-section of quarry, Q, UU; Quaternary deposits and the upper member of the upper formation. UL: The lower member of the upper formation. MU: The upper member of the middle formation. MM: The middle member of the middle formation. T: "Tohri", the zone concentrating with the altered volcanic materials (Miso).

29 N. KOHYAMA AND H. HAYASHI

Table 2. Horizon of quarries in Oya district.

•›: Quarry out Oya-ishi mainly from this strata.

Quarry out Oya-ishi partly from this strata.• :

Quarried out once Oya-ishi from this •¢:strata. tion. In the lowland where has been expolited recently and is eastern area of this district, the quarries consist of vertical shaft to a depth of 100 m and Oya-ishi has dug out from the lower member of the upper formation.

CONSUMPTIONOF OXYGENBY CLAY IN THE QUARRY

The amount of the oxygen consumed per 10 g of Pleistocene gravel and Alluvial deposits in which the accidents due to oxygen deficiency have happened or will possibly happen, were measured by us3-7) and Yamaguchi8,9). According to our data, 10g of Pleistocene gravel and Alluvial deposit were consumed 3.2 ml and 1.04ml of oxygen, respectively. Alluvial deposits include a great deal of organic materials and consist mainly of clay minerals such as montmorillonite, chlorite and illite, and quartz and feldspar. The consumption of oxygen according to Alluvial deposits conincide with the generation of carbon dioxide and methane from them. These mechanisums were described and reviewed in previous paper4,7,10). Oya-ishi contains many volcanic rock fragments which are perfectly altered smectites. These rock fragments called "Miso", are commonly dark blue in colour in unweathered deep places, but easily turn to black spontaneously in air within a few hours and finally to brown in a few weeks. A bluish green samples collected from deep places have been analyzed by various methods. The quantity of oxygen consumed by 10 g of the bluish green coloured samples increased with time. As shown in Fig. 6, 105ml of oxygen were consumed by 10g of the bluish green coloured sample. This sample, of course, turned easily brown. This amount of oxygen consumption of Miso is more than 100 times of Alluvial deposits, and also more than 30 times of Pleistocene gravel in which the accidents due to oxygen deficiency have happened frequently in Tokyo.

30 OXYGEN CONSUMPTION OF CLAY MINERALS

Fig. 6. Amounts of consumed oxygen due to 10 g of Oya samples, Alluvial clays and Pleisto- cene gravel under the normal environment. Note Clay No. 1 & 2: Alluvial Clay (Edagawa-cho) Clay No. 3: Alluvial clay (Kohnan) Gravel: Pleistocene gravel (Gotanda) 6, 7, and 8: Oya samples.

MINERALOGICAL STUDY OF THE CLAY MINERAL, Miso, IN THE QUARRY

We measured about 19% of oxygen in the air at some level of quarries where exposed large amount of Miso in tuffaceous sediments at Oya. It is quite uncommon and interest phenomenon that the clay mineral called Miso has consumed large amount of oxygen. There is still no report about this phenomenon and mechanism. In order to solve this problem, we have undertaken an investigation of the mineralogical properties of the clay mineral, Miso, and discuss mechanism of oxidation due to clay mineral.

Sample The Oya-ishi is vitric tuffacous sediments, and contains the altered volcanic rock fragments, crystal-fragments of plagioclase, quartz, hornblend and biotite, and

31 N. KOHYAMA AND H. HAYASHI

Fig. 7. Photomicrographs of the bluish green glass fragments in Oya-ishi. Note; A: Observed from the direction perpendicular to fluidal texture.

B: Observed from the direction parallel to

fluidal texture. Both are obtained under open nicol.

Fig. 8. Photomicrographs of altered rock fragments called Miso. Note; A: Observed from the direction perpendicular to the vesicular texture (open Nicol). B; Observed from the direction perpendicular to the vesicular texture (cross Nicol). C: Observed from the direction parallel to the vesicular texture (open Nicol). D: Observed from the direction parallel to the vesicular texture (cross Nicol).

32 OXYGEN CONSUMPTION OF CLAY MINERALS aggregates of bluish green glass fibrous fragments. The bluish green glass fragments commonly show a fluidal texture (Fig. 7). Aggregates of the bluish green fibrous materials are composed of fine flakes of fibers about 0.01 mm in mean size, and are frequently replaced by clinoptilolite and celadonite. The altered volcanic rock fragments were identified as an iron rich variety of montmorillonite11). These fragments usually contain a small amount of high-quartz crystals having hexagonal pyramid and aggregates of clinoptilonite. These fragments, so called Miso, are dark green to bluish green in colour on fresh surfaces when they are collected from the inner portions of the walls in deep caves, but easily turn to black spontaneously in air within a few hours and finally to brown in a few weeks. The matrials collected from deep places were designated as unweathered samples. These unoxidized samples were bluish green in colour, but they turn finally brown in air of laboratory after a few weeks. This kind of the samples was denoted by oxidized samples. On exposed surfaces of Oya-ishi in the field, most of these frag ments have already turned brown, but usually they have been discoloured to pale brown, yellow or gray as a whole. These materials were designated as weathered samples which are, of course, oxidized ones. The photomicrographs of the unweathered sample (No. 6-2) are shown in Fig. 8. Miso has vesicular texture and each vesicular takes like a cyrindrical feature being from 0.01 mm to 0.1 mm in its diameter and several mm in its length. The vesicu- lars show dark brown in their core part whereas pale yellowish gray in colour in their margin. Although retardation of them is relatively low, the retardation of the core part is slightly higher than that of the margin of each vesicular. This fact suggests that clay mineral constituting the core part differs slightly from that of the marginal part of each vesicular.

Chemical compositions The chemical compositions of the samples from Oya, together with other member of the smectite, are shown in Table 3. As seen from Table 3, the iron contents of the samples from Oya range from 5 to 15% of their sample weight, and the larger amount of iron in the samples, the deeper colour they are.

Iron in the dark green coloured samples (Nos. 5-1, 6-1, and 9-1) and in the brown coloured samples (Nos. 5-2, 6-2, 9-2 and others) is ferrous and ferric state, respectively. With increasing of Fe2O3 contents in the samples, MgO contents have tendency to increase and conversely Al2O3 tend to decrease in them. The amounts of water expelled below 110•Ž being denoted as H2O(•\) range from 30 to 50% of sample weight of unoxidized ones. The dark green coloured samples have relatively large amount of above mentioned water than the brown coloured samples. It is well known that the theoretical formular of the smectite without consider- ing lattice substitution is Al2Si4O10(OH)2.nH2O, and theoretical composition without the interlayer material is SiO2: 66.8%; Al2O3: 28.3%; 1-1,0(+): 5%. However, smectites always differ from the theoretical formular, because the lattice is always

33 N. KOHYAMA AND H. HAYASHI

Table 3. Chemical compositions of Oya-samples and some smectites.

ox : oxidized. unox : unoxidized, uw: unweathered, w: weathered, ac: treated with HCl. S : Montmorillonite, Oya, Utsunomiya, Tochigi Prefecture; analysis from Sudo and Ota16). a : Montmorillonite, Wyoming bentonite, Upton; analysis from Ross and Hendricks12). b : Beidellite, Black Jack Mine, Carson County, Idaho; analysis from Nagelschmidt13). c : Nontronite, Vehenjy, Madagscar; analysis from Nagelschmidt13). d : Saponite, Silver Bay, Minesota; analysis from Whelan and Lepp14). e : Hectorite. San Bernardino County. California: analysis from Nagelschmidt13). f : Cardenite, Carden Wood, Aberdeemshire; analysis from MacEwan15). g : Iron-rich saponite (Lembergite), Moniwa, Miyagi Prefecture; analysis from Sudo16). h : Iron-rich montmorillonite, Hanaoka Mine, Akita Prefecture; analysis from Sudo17). A : Beidellite, Aterazawa, Yamagata Prefecture; analysis from Hayashi18). N : Nontronite, Spokane, Washington; analysis from Ross and Hendricks12). I-S: Iron-rich saponite, Honjo, Fukushima Prefecture; analysis from Kimbara (unpublished).

34 OXYGEN CONSUMPTION OF CLAY MINERALS unbalanced by the substitutions, that is, Mg2+ for Al3+(VI), Al3+(IV) for Si4+, etc.. The smectites depend on the substitution within the lattice, and are classified into principal following member;

Dioctahedral Montmorillonite 0.33 M+(Al1.67Mg0.33) Si4O10 (OH)2 Beidellite 0.33 M+ Al2 (Si3.67Al0.33) O10(OH)2 Nontronite 0.33 M+ Fe2 (Si3.67Al0.33) O10(OH)2

Trioctahedral Saponite 0.33 M+ Mg3 (Si3.67Al0.33) O10(OH)2 Sauconite 0.33 M+ (Mg, Zn)3 (Si3.67Al0.33) O10(OH)2 Hectrite 0.33 M+ (Mg, Li)3 (Si, Al)4 O10 (OH)2 Both the bluish green coloured- and the brown- coloured samples differ from montmorillonite and/or beidellite, because SiO2 and Al2O3 contents of both samples are poor than those of montmorillonite and beidellite. Substitutions within the octahedral sheet of the smectites may vary from few to complete. Total replacement of 2Al3+ by 3Mg2+ yields the mineral saponite, replacement of aluminium by ferric iron yields nontronite. These samples used in this study are richer in Al2O3 contents and poor in Fe2O3 contents than those of nontronite, and furthermore they contain larger amounts of Al2O3 and extremely smaller amounts of MgO than those of saponite and/or iron-rich variety of saponite.

Mossbauer effect The two main parameters of a Massbauer spectrum are the isomer shift and the quadrupole splitting. The two parameters are sensitive to the oxidation state, electronic configuration, co-ordination number and site symmetry of the iron atom. The isomer shift is mainly related to chemical bonding and chenges in valence. The quadrupole splitting is sensitive to structural environment. The Mossbauer spectra can be used to determine non-destructively the ferrous and ferric iron contents. The Mossbauer spectra were determined by using the source of Co57 diffused in a Cu matrix. The Mossbauer spectra for the bluish green coloured sample (6-1), its partially oxidized sample (No. 6-1'), and its oxidized brown coloured sample (No. 6-2), together with the dark brown coloured sample (No. 1) which was oxidized in room air, are shown in Fig. 9 and their Mossbauer parameters listed in Table 4. The Messbauer spectrum for the bluish green coloured sample (No. 6-1) shows two peaks at -0.2 mm/sec and + 2.6 mm/sec. These two peaks have an isomer shift and quadrupole splitting characteristics of iron (II). The isomer shift and the quadrupole splitting characteristics of iron (III) are scarecely observed in the bluish green coloured sample. This fact is consistent with data of chemical analysis showing a little amount of Fe2O3 and large amount of FeO.

35 N. KOHYAMA AND H. HAYASHI

Fig. 9. The Mossbauer spectra of Oya samples.

Table 4. Mossbauer parameters of Oya samples.

The partially oxidized sample (No. 6-1') shows that the peak at +2.6 mm/sec decrease in its intensity, the peak at -0.2mm/sec become broad one and new peak at + 0.8mm/sec is appeared. The brown coloured sample (No. 6-2) shows this tendency to diminish progressively peaks due to iron (II) and to augment the peaks due to iron (III). The ratio of Fe3+/Fe2+ of the sample (No. 6-2) was esti- mated to be 5.9 by wet chemical analysis, and the ratio of the peak height in Mossbauer spectrum was about 4.5. Quadrupole splitting of Fe2+ ion decreases gradually with increasing degree of oxidation of iron ion. The isomer shift of Fe2+ and Fe3+ and quadruple splitting of Fe3+ seem to remain unchageable, whereas

36 OXYGEN CONSUMPTION OF CLAY MINERALS quadruple splitting of Fe2+ change from +2.86 mm/sec to 2.52 mm/sec. This suggests that the site symmetry or structural environment for the Fe2+ ion is more sym- metrical in the oxidized state than in the unoxidized one.

Differential thermal analysis Differential thermal analysis curves of the samples from Oya, together with other member of smectites, are shown in Eig. 10. Generally speaking, smectites show a large low-temperature endothermic peak between 100•Ž and 200•Ž, a medium- small endothermic peak at about 700•Ž and a small S-shape endothermic-exothermic peak system at about 850•Ž to 950•Ž. Beidellite, the high aluminium variety of

Ftg. 10. Differential thermal analysis curves of

Oya samples, beidellite and nontronite. Note; N: Nontronite, (Spokane, Washington, U.S.A.) B: Beidellite (Aterazawa, Yamagata Prefecture, Japan). Roman numbers: Oya samples.

Mean heating rate: 10•Ž/min. Sample weight: 200 to 300 mg. Sample holder: Nickel.

37 N. KOHYAMA AND H. HAYASHI smectites, has the dehydroxylation peak between 550•Ž and 700•Ž and disappears the endothermic peak of S-shaped system, but the exothermic peak occurs at just below 1000°C. Nontronite, high iron variety of beidellite, yields a curve with a general resemblence to that of montmorillonite, however, the endothermic peak of

dehydroxlation appears between 400•Ž and 500•Ž. The presence of much iron

depress the temperature of the dehydration peak that obtained for beidellite.

Differential thermal analysis curves of the samples from Oya are recognized first

endothermic peak between 100•Ž and 200•Ž, a endothermic peak between 650•Ž

and 700•Ž, a weak or no endothermic peak between 800•Ž and 900•Ž followed by

a weak exothermic peak. In these samples, the characteristic endothermic peak

between 400•Ž and 550•Ž of nontronite can hardly detected, but the presence of

aluminous montmorillonite can be recognized by existence of charcteristic endo-

thermic peak at about 700•Ž, and any other peaks due to impurities such as iron

oxides can not be recognized. The slight differences of peak temperature and

sharpness between the samples from Oya are considered to be mainly caused by

variations of the chemical compositions, that is, the endo- and/or exo-thermic peaks

become less clear compared with the increasing the content of Fe2O3. The thermal

study of the samples confirms the fact that the clay minerals in Miso are recognized as smectite without the impurities of iron oxides and typical nontronite.

Infrared absorption spectra Infrared absorption spectra of Oya samples and beidellite are shown in Fig. 11. The smectites show a broad absorption band at about 3300 cm-1 to 3500 cm-1 which is ascribed to the existence of interlayer water, and the OH stretching band at 3620 cm-1 to 3645 cm-1 in montmorillonite-beidellite. Substitution of Fe+ for octahedral Al3+, as in nontronite, causes a striking shift of OH band to lower frequency. The absorption band due to the OH stretching vibration of aluminous montmorillonite and nontronite is observed at 3625 cm-1 and 3565 cm-1, respectively. Unweathered iron-rich samples (Nos. 6-2, 7 and 8) show a broad band at about 3615 cm-1 showing the wave number are slightly smaller than that of montmorillonite-beidellite. It may be seen that they are intermediate values between those of montmorillonite and nontronite. When they are treated with 0.5 N HC1, the frequencies of the OH stretching are slightly increased such as from 3615 cm-1 to 3626 cm-1 in the sample No. 7 and 3617 cm-1 to 3625 cm-1 in the sample Nos. 6-2 and 8.

In the region between 1300 cm-1 and 400 cm-1, all of the bands are coincide with aluminous montmorillonite except the band at 670 cm-1. The bending vibration of OH groups associated with Al3+ ion occurs near 920

cm-1; those associated with Fe3+ ion absorb near 820 cm-1. If they associated with

an Al3+•\Fe3+ pair, it occurs in the region 845 cm-1 and 890 cm-1. The latter band

is dominant in smectites which has a particularly high iron contents. In this region,

38 OXYGEN CONSUMPTION OF CLAY MINERALS

Fig. 11. Infrared absorption spectra of the natural and acid treated Oya samples and beidellite. Note;R: Beidellite from Rokkaku, Yamagata Prefecture. 6-2, 7 & 8: Samples from Oya, Tochigi Prefecture. -0: Natural sample. -1 & 6-2-3: Sample treated

with HCl.

nontronite has two characteristic bands at about 820 cm-1 and 675 cm-1, while trioctahedral smectite such as saponite and stevensite have a band at about 670 cm-1. Since a characteristic band at about 820 cm-1 of nontronite is not recognized and only the band at about 670 cm-1 is observed in Oya samples, there is a pos- sibility of containing some of trioctahedral smectite. The band at 670 cm-1 is easily disappeared by HCl treatment, as shown in Fig. 10. This fact coincides well with the behaviour of some of the (060) reflection in the X-ray diffraction patterns of Oya samples; that is, sample No. 6-6' treated with HCl for a few hours have disappeared the larger peak of (060) reflction. This treated sample, of course, has no infrared absorption band at 670 cm-1. These facts suggest that a smectite having a larger unit cell is easily destroyed by HCl treatment, but another smectite having a smaller unit cell is remained by HCl treatment, and the samples from Oya have two kinds of smectites.

RA N. KOHYAMA AND H. HAYASHI

X-ray study The X-ray powder patterns of the samples from Oya, beidellite and nontronite are shown in Fig. 12. The X-ray diffraction patterns of the samples from Oya agree with that of smectite, and the pale yellow coloured samples are sharp but the brown coloured samples have somewhat broad and obscure patterns. Any other impurities such as iron oxides are not recognized in these patterns. It may be said that the X-ray diffraction pattern becomes indistinct with increasing of the amount of iron in a sample.

Fig. 12. X-ray diffraction patterns of Oya samples,

beidellite and nontronite. Note; A: Beidellite (Aterazawa, Yamagata Prefecture, Japan). N: Nontronite (Spokane, Washington, U.S.A.). 1, 6-2 and 7: Oya samples.

To examine the whole iron is truly in the crystal structure of smectite or not, intensities of (001) are measured in detail. Natural smectite has one molecular water layer when the exchangable cation is M+ and two molecular water layer when it is M2+ in the interlayer. The former show a c-axis spacing of about 12.5A and the later from about 14.5 to 15.5A. Whereas dehydrated smectite has no water layer in the interlayer and a c-axis spacing of about from 9.5 to 10A. A correlation of the effect of substitutions of iron in the octahedral sheet of smectite and the intensities of the (00l) reflections is more clearly observed in the dehydrated form than that of the naturally hydrated form. That is, the intensities of (001) reflections of naturally hydrated smectite are mostly influenced by the amount of interlayer water rather than that of the octahedral iron, whereas the

40 OXYGEN CONSUMPTION OF CLAY MINERALS dehydrated smectite showing a (001) reflection at about 9.8A has no interlayer water and considerable clear and strong basal reflections of the higher order such as (002) and/or (003) reflection. They are mainly influenced by the substitutions of the octahedral sheet. The effect of substitution in the octahedral sheet of dehydrated smectite is calculated as follows : If the smectite is a dioctahedral member, a highly aluminous member has a similar intensity of (003) and (002) reflection and the ratio of I(003)/I(002) increases along with the increasing of the substitutions of iron in the octahedral sheet. The feature is clearly shown in the oriented X-ray diffraction patterns in Fig. 13; A,300•Ž means a dehydrated form of beidellite from Aterazawa and N, 300°C means a dehydrated form of nontronite from Spokane, Washington. Both peaks of (002) and (003) are cleraly observed on the A, 300•Ž, but a peak of (002) can not be seen on the N, 300•Ž.

If the smectite is a trioctahedral variety, the (002) reflection is extremely weak compared with the (003) reflection. The feature of the basal reflections for samples of Oya rich in iron (Nos. 7

Fig. 13. X-ray diffraction patterns of Oya samples, beidellite and nontronite in natural and heated state. Note; A: Beidellite from Aterazawa, Yamagata Prefecture. N: Nontronite from Spokane, Washington, U.S.A. 7 & 8: Samples from Oya, Tochigi Prefecture.

41 N. KOHYAMA AND H. HAYASHI

42 OXYGEN CONSUMPTION OF CLAY MINERALS

43 N. KOHYAMA AND H. HAYASHI and 8) are also shown in Fig. 13. The intensity of (002) reflection is obviously weak and the ratio of I(003)/1(002) are evidently larger than that of aluminous montmorillonite and smaller than that of nontronite. The fact suggests that the iron composed in the samples is not a impurity and/or a mixture of iron oxide but contained in a crystal structure of smectite. There is an important difference in the X-ray diffraction patterns between the samples from Oya and the ordinary member of the smectites. Some of the samples from Oya have the double peak at the (060) and (400) reflection. The spacings of hk reflections of the samples from Oya, together with the member of the smectites, are given in Table 5. Indices19) are those for a two-dimensional orthohexagonal lattice a=5.21A and b=9.02A, or a=5.32A and b=9.22A. The detail (060) reflection of the samples from Oya are shown in Fig. 14. The samples are classified into two groups by the feature of (060) reflection. First group shows a similar X-ray diffraction pattern to that of ordinary smectite. All of the weathered- and some of the unweathered-samples having small amount of iron (Nos. 2, 3, 4, 5-1 and 5-2) have a single peak of (060) and (400) reflection.

Fig. 14. (060) reflections of the samples from Oya. Notation is similar to that of Table 3.

44 OXYGEN CONSUMPTION OF CLAY MINERALS

The a- and b-parameter of them is about 5.2A and 9.0A, respectively. Second group shows the double peaks of (060) and (400) reflection. The samples belonging to this group contain a considerable large amount of iron (Nos. 1, 6-2, 7,8 and 9-2).

From these doublets, the a-parameters are calculated as about 5.2181.and 5.3A, respectively, and b-parameters are obtained as about 9.0A.and 9.2A, respectively. In general, dioctahedral and trioctahedral smectite can be distinguished by the b- parameter. That is, dioctahedral smectite has b-parameter of about 9.0•\9.13A, whereas trioctahedral smectite has it of about 9.16•\9.2A. These values of both a- and b-parameters are given in Table 5. These facts suggest that the unweathered samples having larger amount of iron should be composed of the mixture of two kinds of smectite. The smaller unit cells of Oya samples are considered to resemble those of montmorillonite or beidellite, and the larger unit cells to resemble those of Cardenite or Lembergite which belong to iron-rich saponite. They are given in Table 5. The (060) reflection of the samples from Oya, together with the artificial mixture of nontronite and beidellite, at natural and heated state are shown in Fig. 15.

The intensities of the (060) reflections due to nontronite and beidellite of the mixture gradually weakened with increasing temperature. When the mixture was heated between 500°C and 600°C for one hour, the (060) reflections of notronite and beidellite changes into mono-reflection. Neverthless, Oya samples (Nos. 7 and

9-2) have the (060) reflection at about 1.52-1.53A until 700•Ž. These double peaks at the (060) reflection of Oya samples resisted against heat treatment to extent of considerable higher temperature than that of mixture of nontronite and beidellite.

Fig. 15. The changes of the (060) reflections of Oya samples (Nos. 7 and 9-2) and artificial mixture (N-M) of beidellite and nontronite on heating.

45 N. KOHYAMA AND H. HAYASHI

Fig. 16. The changes of the (060) reflections of Oya samples (No. 6, 9 and 10) owing to spontaneous oxidation and/or HC1 treatment. Note; 6-1, 9-1 and10-1: Unweathered samples. 6-1', 6-2, 9-2, 10-2: Oxidized samples. 6-6': Sample treated with HC1.

It suggests that the larger peak of (060) reflections is unable to ascribed to normal nontronite but a kind of trioctahedral smectite. The effect of HC1 treatment on the (060) reflections of the Oya sample is shown in Fig. 16. When the sample (No. 6-2) treated with HC1, the larger value of the (060) reflections disappeared and smaller one was remained in the treated sample (No. 6-6') as shown in Fig. 16. Change of the value of (060) reflections of Oya samples during the spontaneous oxidation is also observed. The doublet at the (060) reflection was shifted toward high angle of 2ƒÆ, as shown in Fig. 15, by spontaneous oxidation in room air along with change in colour from deep blue to brown. The large values of them become to decrease more acute than that of the smaller one during oxidation, as follows;

11.549A (6-1)•\1.540A(6-1')•\1.534A (6-2)

1.504A(6-1)•\1.501A(6-1')•\1.500A (6-2)

1.549A (9-1)•\1.538A (9-2)

1.507A(9-1)•\1.504A (9-2)

1.547A(10-1)•\1.531A (10-2)

1.504A (10-1)•\1.501A (10-2)

46 OXYGEN CONSUMPTION OF CLAY MINERALS

Fig 17. X-ray images for some elements of Oya samples.

47 N. KOHYAMA AND H. HAYASHI

This phenomenon suggests that the iron in the samples is contained in the crystal structure of the two kinds of smectites, and ferrous iron in the unoxidized samples are spontaneously oxidized to ferric iron in the air acompanied with shrink of their unit cells. Of course, the iron after oxidized is composed in the crystal structure of the smectites.

Electron probe microanalysis The altered volcanic rock fragments called Miso show vesicular texture having two parts. The central part is of brown in colour and the outer part is pale yellowish gray in colour. All two phases show relatively low retardation. The identification of the Miso as two kinds of iron-rich smectites was confirmed by X-ray analysis. The polished disk of the sample (No. 6-2) were examined by electron probe microanalysis using a Shimazu EMX-1 microanalyser with an excitation voltages of 15 KV. The electron beam scanning micrographs and photo- micrograph of the Miso are shown in Fig. 17. X-ray scanning images from the electron probe show the distribution of elements such as Si, Al, Fe, Mn, Mg, Ca, Na, and K, in the area selected for analysis. It can be observed same texture between the microphotograph and the secondary electron image of the sample (No. 6-2), however, the bright parts in the secondary image correspond to the dark part in the microphotograph being under the open nicol. No impurities such as iron oxides, film of iron gel and so on are observed by the secondary electron image.

Fig. 18. Line scanning figure of Oya sample.

Microprobe traverses were made across same vesicular texture of the sample, showing brighter core surrounded by dark narrow bands by the observation of the secondary electron image. The antipathetic iron-aluminium relationship is clearly shown in the sample as seen in Fig. 18; that is, the core parts of vesicular showing dark brown colour under the photomicroscope are richer in Fe2O3 (or FeO when the sample was unoxidized in air) and poorer in Al2O3 than the marginal parts. The value of Fe2O3 contents in the core parts is about 30% of the sample weight

48 OXYGEN CONSUMPTION OF CLAY MINERALS and the marginal parts is about 5 to 8%, whereas Al2O3 is about 5% and 15%, respectively. The results obtained by this analysis and X-ray analysis suggest that the materials in central parts of vesicular consist of iron-rich trioctahedral smectite, and the material of marginal parts consist of iron-rich dioctahedral smectite.

DISCUSSION

There are considerable amount of ferrous iron in the altered volcanic fragments called Miso in tuffaceous sediments which situated in deep places at Oya. The results of D.T.A. and X-ray analysis shows that the altered materials are composed of smectites without any other impuriteis such as iron oxides. Sum- marizing the data given so far, it may be concluded that the altered volcanic rock fragments are identical with the mixture of two kinds of iron-rich smectites. A measurement of the (060) spacing, microscopic observation and E.P.M. analysis of Miso indicate that these two smectites are dioctahedral iron-rich smectite and trioctahedral iron-rich smectite. The ferrous iron seems to substitute di- and/or trioctahedral site of the smectite. The mixing ratio of dioctahedarl and trioctahedral smectite differs from sample to sample. The detailed studies about characteristics of these minerals will be appeared another paper in the near future. Mineral oxidation is of two radically different kinds. Oxidation of minerals is accomplished by addition of oxygen and complete destruction of the original mineral. In all of these cases the original mineral is destroyed and one or more new minerals are formed by oxidation. Pyrite or marcacite (FeS2) are transformed into iron oxides producing sulfuric acid by oxidation. The processes are so well known that further description is needless. This phenomenon is one of causes of the accidents due to oxygen deficiency in the sulphur mine. Another oxidation takes place in minerals which accompanied with loss of hydrogen but never any considerable changes in the structure of the original mineral. Many studies on oxidation in minerals are those performing under heat treatment. Addison et al.20,21) have extended the ideas of Brindley and Youell22) on the mechanism of oxidation. Addison and Sharp21) proposed that when a mineral is heated in oxygen or air, the behaviour can be represented as follows. 4Fe2++4OH-+O2=4Fe3++4O2-+2H2O This equation represents the simultaneous oxidation of iron (II) and hydroxyl, and is primary reaction: there are no major change in the crystal lattice according to this reaction. This reaction requires additional oxygen which is introduced during experiment or may be drived from the air. Under normal temperature and environment, oxidation in mineral requires long time. Schaller and Vlisidis23) reported spontaneous oxidation of powdered siderite (FeCO3). According to them, initial ferrous content in powdered siderite was 59.42%, and was being spontaneously decreased as a function of time. About 45 years after

49 N. KOHYAMA AND H. HAYASHI the initial analysis, most of ferrous iron have spontaneously oxidized to ferric iron. Keller24) reported that oxidation of iron in montmorillonite occurred sufficiently during laboratory grinding. In the case of Miso from Oya, the ferrous iron in the lattice of the smectites which belong to dioctahedral and trioctahedral smectite, easily turn to ferric iron in an exposed environment, so that ferrous smectite is unstable in a normal environment. Fieled measurment of Eh have been made on the suspension which particles of

Miso was dispersed in distilled water. Fresh fragments with deep blue in colour show extremely small value indicating a reducing condition, whereas the black to brown coloured samples show large Eh values indicating an oxidizing condition. From this measurement, the Miso situated in deep places may stand under reducing condition. This finding supports that ferrous irons occupy in octahedral lattice of the smectites. The Miso situated in deep places is mixture of ferrous dioctahedral smectite

and ferrous trioctahedral smectite. The oxidation of Fe2+ to Fe3+ produces an in-

crease in positive charge in the crystal structure which must be blanced by in-

creasing of negative charge. Such an increase can be achieved by a gain of O2-

or by the oxidation of OH- to from O2- accompanied by elimination of the hydrogen

as water. OH- and O2- are similar in size, little change in structure is necessary

except a decrease in lattice parameters caused by producing Fe3+ ion of which

the size is smaller than Fe2+ ion by oxidation. The unit cell of ferrous smectite

in Miso become to shrink in normal environment, as shown in Fig. 15. This find-

ing is compatible with the data obtained by Brindley and Youell22). They heated

the ferrous chamosite at 400•Ž for 2 hr. The lattice parameters of the ferric

chamosite which was oxidized by heat treatment, were slightly smaller than those

of the original ferrous chamosite, but the primary structure remained unchanged. The iron in the ferrous and ferric smectites from Oya are located in the octa- hedaral site. It is important feature that ferrous and/or ferric iron is sandwiched between two sheets composed of both O2- and OH-. When ferrous smectites being stable under reducing environment, are exposed in air, they have a tendency to change towards the ferric smectites which are stable under the normal environment. In this reaction, oxidation of ferrous iron to ferric iron may be accompanied with decomposition of the hydroxyl group in lattice, and the reaction requires additional oxygen from the air under the normal condition.

ACKNOWLEDGMENT

The writers wish to express their sincere thanks to Professor T. Sudo of Tokyo University of Education, and to Dr. H. Sakabe of National Institute of Industrial Health for suggesting this investigation as well as for constant guidance in the course of the work, and to Dr. S. Shimoda of Tokyo University of Education for the discussions of this problem. We are also indebted to Dr. H. Sano of Ochanomizu

50 OXYGEN CONSUMPTION OF CLAY MINERALS

Womem University for his valuable advices and providing the Mossbauer spectra, and to Mr. Y. Tanaka of Shimazu Seisakusho Ltd. for the Electron Probe Micro- analysis of the sample.

REFERENCES

1) Ota, S. (1949). J. Geol. Soc. Japan, 55, 85. (in Japanese with English abstract). 2) Ota, S. and Sudo, T. (1949). J. Geol. Soc. Japan, 55, 242. (in Japanese with English abstract). 3) Hayashi, H., Ishi, M. and Aoki, S. (1967). Professor Hidekata Shibata Memorial Volume. 297. (in Japanese with English abstract), Shibata Hidekata Kyoju Taikankinenkai, Tokyo. 4) Hayashi, H. (1967). Anzen Kogaku, 6, 31. (in Japanese). 5) Hayashi, H. (1968). Ind. Health, 6, 165. 6) Hayashi, H. and Kohyama, N. (1971). Proc. XIV International Congress on Occupational Health, Tokyo, 701. 7) Hayashi, H. (1972). Memoirs Geol. Soc. Japan, No. 7, (in press), (in Japanese with English abstract). 8) Yamaguchi, H. (1965). J. Ind. Hyg. Japan, No. 4, 31. (in Japanese). 9) Yamaguchi, H. (1967). Anzen Kogaku, 6, 39. (in Japanese). 10) Hayashi, H. (1972). Jiban to Chikasui ni kansuru Kogai, (Land Subsidence and Ground- water) p. 37. Geol. Soc. Japan, Tokyo. 11) Sudo, T. and Ota, S. (1952). J. Geol. Soc. Japan, 58, 487. 12) Ross, C.S. and Hendricks, S.B. (1945). Minerals of the Montmorillonite Group, U.S.G.S. Proffessional Papar 205-B. U.S. Government Printing Office, Washington. 13) Nagelschmidt, G. (1938). Mineral. Mag., 25, 140. 14) Whelan, J.A. and Lepp, H. (1961). Am. Mineral., 46, 430. 15) MacEwan, D.M.C. (1954). Clay Minerals Bull., 2, 120. 16) Sudo, T. (1954). J. Geol. Soc. Japan, 60, 18. 17) Sudo, T. (1950). Proc. Japan Academy, 26, 91. 18) Hayashi, H. (1963). Clay Sci., 1, 50. 19) MacEwan, D.M.C. (1961). The X-ray Identification and Crystal Structures of Clay Minerals, (Edited by Brown G.), p. 143. Mineral. Soc., London. 20) Addison, C.C., Addison, W.E., Neal, G.H. and Sharp, J. H. (1962). J. Chem. Soc., 1468. 21) Addison, W.E. and Sharp, J.H. (1962). Clay Minerals. Bull., 5, 73. 22) Brindley, G.W. and Youell, R.F. (1953). Mineral. Mag., 30, 57. 23) Schaller, W.T. and Vlisidis, A. (1959). Am. Mineral., 44, 433. 24) Keller, W.D. (1955). Am. Mineral., 40, 348.