Chapter 5 Kaolin minerals

Chapter 5 Kaolin minerals

Keinosuke NAGASAWA

Kaolin minerals occur widely as products of hydrothermal alteration and weathering and as constituents of sediments. Their distribution, modes of occurrence and properties, and the interrelationships between them have been the subject of many studies. These minerals are important raw materials for the ceramic, paper, and other industries, and are mined in many places. The economically important kaolin deposits have been summarized by Muraoka et al. (1958), Nagasawa et al. (1969), Fuji (1976), Minato (1976), and Nagasawa (1976). In this Chapter, a general review of the occurrence and properties of kaolin minerals, not restricted to those found in economically important deposits, is given together with a discussion of their genesis. The kaolin minerals dealt with here consist of kaolinite, dickite, nacrite, and halloysite. The nomenclature for halloysite has been a matter of dispute for many years. As described below, the present author (Nagasawa and Miyazaki, 1976) showed that all halloysites examined by him were in a fully hydrated state if they were examined without prior drying. This seems to confirm the opinion of Bates (1952) that halloysite (2Hz0) can be formed only by the dehydration of halloysite (4Hz0). In this article, therefore, the name halloysite is used to denote the 10 A material. 5.1.

DICKITE AND NACRITE

5.1 .I. Occurrence

Dickite and nacrite have been most frequently reported from the so-called “Roseki” deposits. In Japan, especially in its western part, there are many Roceki deposits. These were formed as a result of hydrothermal alteration of various rocks, mainly acidic and intermediate volcanic and pyroclastic rocks of Cretaceous to Miocene age, and consist mainly of pyrophyllite and quartz often associated with kaolin minerals, diaspore and muscovite, although in some cases the kaolin minerals predominate over the pyrophyllite. Four kaolin minerals, kaolinite, dickite, nacrite and halloysite, have been reported from these deposits. Yoshiki (1934) first identified the kaolin mineral in the Shokozan area, Hiro189

190

KAOLIN MINERALS

shima Prefecture, as dickite on the basis of its optical and thermal properties. The Roseki deposits of the Shokozan area were later studied by Iwao (1949), Matsumot0 (1968), etc. According to them, they represent stratiform deposits formed by replacement of Cretaceous dacite and dacitic tuff, and consist of a pyrophyllite zone and an overlying kaolin-alunite-quartz zone, both of which are surrounded by a zone of silicification containing hematite and pyrite (Fig. 5.1). Dickite occurs in the kaolin-alunite-quartz zone as lenticular masses or veins sometimes associated with nacrite, diaspore, or alunite (Takeshi, 1958; Iwamoto, 1963; Matsunioto, 1968).

Silicification zone impregnated with Fe minerals

Pyrophyllite zone

--

Corundum-diaspore-pyrophyllite

Alunite-Kaolin zone

zone

a

Silicification zone Weakly altered wall rock

Fig. 5.1. Schematic cross-section showing the alteration zoning at the Shokozan mine, Hiroshima Prefecture. The iron mineral in the silicificationzone impregnated with Fe minerals is usually hematite in the zone on the hanging wall, and pyrite in that on the footwall. (After Matsunioto, 1968.)

Dickite has also been reported from many other Roseki deposits, e.g. Takatoku, Tochigi Prefecture (Kodama, 1963); the Kanakura and Kobayashi mines, Nagano Prefecture (Iwai et al., 1949; Takeshi, 1958); the Hiraki mine (Tanaka et al., 1963), Ebara mine (Ueno, 1964; Yamamoto, 1965), Kiyotaki mine (Ueno, 1964), Shinagawa-Sampo mine (Takeshi, I958 ; Ueno, 1964) and Fukuyama mine (Takeshi, 1958; Ueno ef al., 1958), Hyogo Prefecture; and the Rissho mine (Yamamoto, 1965) and Kato mine (Mitsuishi area) (Sugiura and Nakano, 1960), Okayama Prefecture. In these cases, the dickite usually occurs as fillings in the interstices of aggregates of diaspore, as veinlets, or as massive aggregates. Nacrite is also found in Roseki deposits, both associated and not associated with dickite. Examples include the Otoge mine, Yamagata Prefecture (Tanemura and Horiuchi, 1958); Takatoku, Tochigi Prefecture (Kodama, 1963); the Kobayashi and Yonago mines, Nagano Prefecture (Iwaj et al., 1949; Takeshi,

DICKITE AND NACRITE

191

1958); the Ebara mine (Yamamoto, 1965) and Shinagawa-Sampo mine (Takeshi, 1958), Hyogo Prefecture; and Shokozan area, Hiroshima Prefecture (Takeshi, 1958; Iwamoto, 1963). Occurrences of dickite and nacrite due to younger volcanic activity have been recognized. The kaolinization often occurred in association with alunite or silica deposits and with sulfur deposits of both Quaternary and Pliocene age. A typical example of these deposits is seen in the Ugusu mine, Shizuoka Prefecture, as shown in Fig. 5.2 (Iwao, 1962, 1968; Uno and Takeshi, 1977). Here, silica deposits were formed by hydrothermal alteration due to former geothermal activity in a period after the Pliocene. Zonal alteration, i.e. silica zone (central part)+alunite zone-+clayey zone+original rock (Miocene propylite) is well developed, and dickite represents a principal component of the inner portion of the clayey zone sometimes in association with nacrite. Dickite has been reported from the Itaya mine, Yamagata Prefecture, where it occurs in altered pyroclastics composed of quartz, alunite and kaolin minerals (Honda, 1964; Togashi and Fujii, 1972; Togashi, 1976). Nacrite, associated with dickite, is also known from the Itaya mine area (Honda, 1964). In an active geothermal area at Otake, Oita Prefecture, dickite occurs as a constituent of an alteration zone characterized by kaolin and pyrophyllite (Hayashi, 1973). At the Kasuga and Akeshi mines, Kagoshima Prefecture, nacrite and dickite have been reported to occur in association with gold mineralization (Tokunaga, 1954, 1955, 1957). Here, stockwork and impregnation deposits of gold, enargite, luzonite, pyrite, etc. are found in a zone of silicification which is surrounded by a dickite zone and then a kaolinite zone. The nacrite occurs as veinlets without metallic minerals and as a minor constituent of the dickite zone. Other examples of dickite occurrence associated with metallic mineralization have been reported

Am1 I I l l I I l l I I

400-

1

/.

.:

0-..-O-

100

200,

Silica zone

n

Altrnite zone

Ix_I Propytite

Clayey zone

Fig. 5.2. Cross-section of the silica deposit at the Ugusu mine, Shizuoka Prefecture. (After Iwao, 1970.)

192

KAOLIN MINERALS,

TABLE 5.1 Chemical analysis data of dickite SiOz TiOz Ah03 Fez03 FeO MnO MgO CaO NazO KzO HzO+ HzO Ig. loss Total SiOz/A1203

Hokugo 45.62 38.92 1.03 tr. 0.12 0.08

Mitsuishi

Ebara

45.42 0.02 38.78 0.88 0.04

45.31 0.00 40.17 0.14

Shokozan 45.99 0.21 39.34 0.01

] 13.98

0.86 0.12 tr. tr. 13.42 0.54

0.00 tr. 0.00 0.24 0.01 13.89 0.35

99.75

100.08

100.11

14.45 100.06

1.99

1.99

1.91

1.98

0.06

-

Hokugo: Hokugo-mura, Miyazaki Prefecture (Matsukuma and Tanaka, 1955). Mitsuishi: Kato mine, Mitsuishi, Okayama Prefecture (Sugiura and Nakano, 1960). Ebara: Ebara mine, Hyogo Prefecture (Ueno, 1964). Shokozan: Shokozan mine, Hiroshima Prefecture (Matsumoto, 1968).

TABLE 5.2 Chemical analysis data of nacrite SiOz TiOz A1203 Fez03 FeO MnO MgO CaO NazO KzO HzO HzOTotal

+

Yonago 41.52 tr. 37.51 1.59 0.92 0.92 0.64 14.54 0.93 98.57

Otoge

Kanagato

44.52 tr. 39.91 0.09 0.01

45.17 0.04 40.24 0.02

0.42 0.14 0.03 0.08 14.34 0.93 100.47

tr. 0.30 0.40 0.06 0.12 14.13 0.10 100.58

1.88 1.90 1.89 SiOziA1~03 Yonago: Yonago mine, Nagano Prefecture (Twai era!., 1949). Otoge: Otoge mine, Yamagata Prefecture (Tanemura and Horiuchi, 1958). Kanagato: Kanagato mine, Yamaguchi Prefecture (Minato, 1976).

KAOLINITE AND HALLOYSITE

193

from stibnite veins at Hokugo, Miyazaki Prefecture (Matsukuma and Tanaka, 1955), a gypsum-anhydrite vein at the Oe lead-zinc mine, Hokkaido (Urashima and Sato, 1967; Nagasawa et al., 1976), Sn-W veins at the Akenobe mine, Hyogo Prefecture (Nagasawa et al., 1976), and the wall rock of the hematite ore at the Akatani iron mine, Niigata Prefecture (Imai, 1960). Nacrite has also been reported from the Kanagato copper mine, Yamaguchi Prefecture, where it occurs as veinlets in kaolinized wall rocks (Minato, 1976). Sugiura and Nakano (1960) have reported dickite at Tomi near Omi, Niigata Prefecture, where it fills a cavity in limestone associated with a small amount of quartz. On the walls of the cavity, the limestone has become transluscent due to recrystallization. 5.1.2. Mineralogical properties Chemical analysis data for dickite and nacrite are given in Tables 5.1 and 5.2, respectively. All the listed samples have smaller values for the molar SiOz/Ale03 ratio than ideal. Examples of X-ray powder diagrams of dickite and nacrite are given in Fig. 5.3. They show the characteristic patterns of these minerals. Takeshi (1958) has pointed out that there is a variation in structural integrity in dickite: that accompanied by diaspore tends to have more ordered structure. Infrared absorption spectra for dickite and nacrite from the Shokozan area are shown in Fig. 5.4. Kodama and Oinuma (1963) and Oinuma and Hayashi (1968) reported that nacrites from near Takatoku and from the Kasuga mine show essentially the same spectral features as in the figure. According to the latter authors, the OH stretching absorptions for the Takatoku material have frequencies of 3700, 3649, and 3629 cm-l, among which the last is the most intense. 5.2. KAOLINITE AND HALLOYSITE

5.2.1. Occurrence: hydrothermal

Kaolinite is an important hydrothermal mineral and occurs abundantly in hydrothermally altered rocks. The Roseki deposits mentioned in section 5.1.1 contain kaolinite as an ixportant constituent. In the Roseki deposits of the Mitsuishi area, Okayama Prefecture, the largest Roseki mining area in Japan, kaolinite occurs in ciose association with pyrophyllite and sometimes with diaspore, and forms massive bodies or veins in ordinary Roseki composed of pyrophyllite and quartz (Kimura, 1951;Yamamoto, 1959, 1965). Some other Roseki deposits consist mainly of kaolinite instead of pyrophyllite, the latter being absent or not important

194

A

ic 20

KAOLIN MINERALS

25

35

40

2 E (CuKa)

Fig. 5.3. X-ray diffraction diagrams of nacrite from the Yonago mine, Nagano Prefecture (A) and dickite from the Shokozan mine, Hiroshima Prefecture (B). (After Nagasawa et nl., 1969.)

in them. The Hiraki mine (Tanaka et al., 1963) and Ebara mine (Ueno, 1964; Yamamoto, 1965), Hyogo Prefecture, are examples. At the Yuri mine, Hyogo Prefecture, halloysite occurs as veins in kaolinite-type Roseki (Ando, 1952). “Toseki”, an important raw material for pottery in Japan, is composed of quartz, muscovite and/or kaolinite. Well-known Toseki deposits occur in the Amakusa Islands, Kumamoto Prefecture, where rhyolite dykes have been altered to Toseki. Togashi (1974) revealed the following zoniilg in one of the Amakusa deposits : carbonate zone (core of the dyke)+clay mineral zone-+ silicification zone+wealdy altered zone (margin of the dyke). All four zones contain muscovite, usually interstratified with expandable layers, and kaolinite.

KAOLINITE AND HALLOYSITE 40

:

36

A

I

Wave number (crn-') I

x 102

I I

"\; dr

i

1

12

195

Y-

4 I

Fig. 5.4. Infrared absorption spectra of nacrite (A) and dickite (B), both from the Shokozan mine, Hiroshima Prefecture. (By courtesy of H. Takeshi.)

Toseki deposits are also known at Izuhara in the Tsushima Islands, Nagasaki Prefecture. In this case, they represent bleached quartz porphyry. White clay composed of kaolinite, halloysite and quartz occurs abundantly as fillings of fissures in the Toseki (Yajima et al., 1970). Kaolinite commonly occurs in altered rocks related to young volcanic activity. Examples include the Itaya mine, Yamagata Prefecture (Togashi and Fujii, 1972; Minato, 1976; Togashi, 1976), the Seta mine, Hokkaido (Komura and Sudo, 1976), the Ugusu mine, Shizuoka Prefecture (Iwao, 1962, 1968; Uno and Takeshi, 1977) (Fig. 5.2), the Beppu mine, Oita Prefecture (Kinoshita and Muta, 1953), Ibusuki, Kagoshima Prefecture (Muraoka, 1951), and the Otake geothermal area, Oita Prefecture (Hayashi, 1973), where kaoljnite is found in association with quartz, cristobalite, or alunite. The Itaya mine is the largest paper clay mine in Japan. The deposits were formed by the alteration of Pleistocene volcanic and pyroclastic rocks as a result of Pleistocene volcanic activity,

196

KAOLIN MINERALS

although Togashi (1976) has shown from radiometric age determinations that in one of the deposits, a basement Miocene tuff is exposed which was altered hydrothermally to muscovite, kaolinite and interstratified micalsmectite in the Miocene. Many volcanic sulfur deposits are known in Japan, especially in northeastern Honshu and Hokkaido. Examples include the Matsuo mine, Iwate Prefecture; Zao mine, Yamagata Prefecture; and the Abuta mine, Hokkaido. They represent replacement deposits composed of iron sulfides and native sulfur and are surrounded by the following alteration zones: a silica or opal zone (inner), alunite zone, kaolin zone, and smectite zone (outer). The kaolin zone consists of kaolinite and halloysite associated with opal (Kinoshita and Muta, 1954; Mukaiyama, 1959; Takeuchi, Takahashi and Abe, 1966). Although the total width of the alteration zones usually reaches scores of meters, more condensed examples are often observed along fissures in compact lava flows. One case is illustrated in Fig. 5.5.

0

5m

Fig. 5.5. Alteration zoning along a fissure in the Nishiazuma sulfur mine, Yamagata Prefecture. 1, Sulfur zone; 2, pyrite zone; 3, opal zone; 4,alunite zone; 5,6, kaolin zone; 7, unaltered rock. (After Mukaiyania, 1959.)

Several hydrothermal halloysite deposits are known. At the Joshin mine, Gunma Prefecture, Quaternary andesite breccia has been altered to tubular halloysite with small amounts of opal and tridymite (Minato and Kato, 1961). At the Iki mine on Iki Island, Nagasaki Prefecture, stratiform halloysite deposits were formed by selective hydrothermal alteration of vitric pyroclastics intercalated in Quaternary basalt flows. The halloysite has a spherical shape (see Fig. 5.12, below) and is associated with cristobalite. The overlying and underlying wall rocks have been weakly altered to form chlorite and smectite (Fujii, 1961; Minato and Utada, 1969). Other examples of hydrothermal halloysite deposits have been reported from the Omura mine, Nagasaki Prefecture (Naga-

KAOLINITE A N D HALLOY SITE

197

sawa et al., 1969), the Okuchi mine, Kagoshima Prefecture (Fujii, 1962; Minato, 1975,1976), and the Rangoshi mine, Hokkaido (Muraoka and Tanemura, 1954). The deposits at the last mine also contain kaolinite. Mitsuda (1960a) found halloysite in the marginal part of a hydrothermal bentonite deposit at Itoigawa, Niigata Prefecture. Halloysite is also known from amygdales in volcanic rocks. Ishibashi (1974) described its occurrence together with zeolites in amygdales in basalt at two localities in Saga Prefecture. Occurrences of kaolinite in altered rocks related to metallic mineralization have been reported from several mines. The Kasuga mine mentioned above is one case. Another important example is the Kampaku mine, Tochigi Prefecture, where gold-quartz veins exist in rhyolite. After the gold mineralization, extensive kaolinization occurred and a silicification zone was formed around the kaolinized rock. The intensely kaolinized rocks have been mined for kaolin clay, which is composed mainly of kaolinite associated with minor amounts of halloysite, alunite, etc. (Mutoh, 1952; Tanemura, 1954). As mentioned above, the hematite replacement deposits of the Akatani mine, Niigata Prefecture, are accompanied by kaolinized wall rocks (Imai, 1960). Kaolinization is also present in the wall rocks of copper-lead-zinc veins at the Mikawa mine near Akatani. Here, the mineralization may be divided into two stages : an earlier sulfide-quartz stage, and a later hematite-carbonate stage. The wall-rock alteration related to the later stage is characterized by kaolinite, quartz, muscovite and siderite (Nagasawa, 1961). At the Mikawa mine, kaolinite occurs also in the veins themselves as fillings of interstices and as veinlets in the sulfide-quartz ore. This kaolinite is closely associated with siderite (Nagasawa, 1953, 1961). Other examples of the occurrence of kaolinite in metallic veins have been reported from the Konomai gold-silver mine, Hokkaido (Urashima, 1953), the Kawaguchi copper mine, Akita Prefecture (Honda and Shiikawa, 1957), the Isobe-Koyama gold-copper mine, Yamagata Prefecture (Isobe et al., 1967), the Toyoha lead-zinc mine, Hokkaido (Shikazono, 1975), etc. In the above examples, the kaolinite is not associated closely with metallic sulfides other than iron sulfides. However, a close association of kaolinite with sphalerite and pyrite has been reported by Sudo and Hayashi (1957), Sudo et al. (1958) and Hayashi (1961) from the Hanaoka mine, Akita Prefecture, and the Kamikita and Aomori mines, Aomori Prefecture, where kaolinite, diaspore, and pyrophyllite (only at Kamikita and Aomori) occur in and around “Kuroko”-type ore bodies. Shirozu et al. (1972) have reported the occurrence of kaolinite, dickite and nacrite in association with black ore (lead and zinc) and pyrite ore in a Kuroko deposit at Matsumine (Hanaoka mine). The occurrence of kaolinite in altered rocks related to Kurokotype deposits has also been reported by lijima (1972a) and Kimbara and Nagata (1 974). Kaolinite occurrence in close association with metallic mineralization is

198

KAOLIN MINERALS

known in certain mercury deposits. Takubo et al. (1954) reported kaolinite as an important constituent of cinnabar veins and their wall rocks in the Yamato mercury mine, Nara Prefecture. Fujiwara and Kujirai (1972) reported cinnabar impregnation in kaolinized sandstone at the Ryushoden mine, Hokkaido. 5.2.2. Occurrence: weathering and sedimentary

Kaolinite is an important product of weathering. In fact, kaolin minerals are the most abundant and widely distributed constituents of Japanese soils (Matsui, 1959; Aomine, 1969). Most soils apart from the volcanic ash soils described in Chapter 2 contain a kaolin mineral as their dominant constituent. Although halloysite with spherical or tubular morphology has been reported in soil (Watanabe et al., 1969), the form of the kaolin mineral in soils is usually platy. Such platy kaolin has sometimes been referred to as metahalloysite due to its low structural integrity (Matsui, 1959; Kato, 1964/65; Nagasawa, 1966). However, the platy morphology suggests that it may be kaolinite. Verification of this will require further detailed mineralogical examinations. In the deeper portions of the zone of weathering, on the other hand, halloysite is a dominant product of weathering. In this case, percolating water is responsible. Shimizu (1972b) examined several weathering profiles of granitic rocks and quartz porphyry, and found that halloysite is the dominant clay mineral in saprolites in contrast to surface soils which are rich in kaolinite. The halloysite has the shape of long tubes. Nakagawa et al. (1972) showed that the feldspar in saprolite from quartz diorite at Senmaya, Iwate Prefecture, had been altered to halloysite. Nagasawa (1966) and Ichiko (1971) examined the clay mineral composition of the Upper Pleistocene marine sand constituting coastal terraces near Nagoya, Aichi Prefecture. The clay fraction of the sand was originally composed of kaolinite, illite and smectite, but it had been altered to tubular halloysite in places where the sand came in contact with percolating water. On the other hand, biotite is known to have been altered to kaolinite associated with hydrobiotite and vermiculite-chlorite intergrades in granitic saprolites (Kakitani and Kono, 1972; Shimizu, 1972b). Kaolinite has also been reported from weathered rocks of various geological ages. At the Iwate clay mine, Iwate Prefecture, the Cretaceous welded tuff underlying Oligocene fresh-water sediments was weathered to a redbed composed mainly of kaolinite, associated in part with gibbsite (Iijima, 1972b). In the area around Nagoya, the basement granite underlying Pliocene sedimentary kaolin deposits was weathered and kaolin minerals were formed from feldspars (Hukuo and Kutina, 1960; Fujii, 1968; Nagasawa and Kunieda, 1970; Shimizu, 1972a). The kaolin minerals consist of platy kaolinite in some places and of long tubular halloysite associated with small amounts of platy kaolinite in others. Both minerals sometimes occur together even within a single exposure (Shimizu, 1972a). The situation at Kakino, Gifu Prefecture, is illustrated in Fig. 5.6. What controls the differential distribution of kaolinite and halloysite is not yet known. The

199

KAOLINITE AND HALLOYSITE

0

6 1

Granite

0

HalbysiU

Fig. 5.6. Distribution of clay minerals in weathered granite under Pliocene “Gaerome” clay at the Kakino mine, Toki, Gifu Prefecture. The amount of clay minerals was estimated by X-ray diffrao tion. (After Shimizu, 1971.)

biotite in the original granite was weathered to kaolinite. The latter is pseudomorphous after the biotite, and is sometimes elongated perpendicular to the basal plane to give a vermicular shape (Mitsuda, 1960b). Studies on the clay minerals in recent marine sediments around the Japanese Islands have been summarized by Oinuma and Kobayashi (1966), Oinuma (1969), and Aoki et a/. (1975). Kaolinite occurs widely as a minor constituent, although the amounts are larger in sediments of the East China Sea (Kobayashi and Oinuma, 1965). The sediments of Lake Shinji, a brackish lake in Shimane Prefecture, have been examined by Fujii and Yasuda (1971). They showed that kaolinite is the dominant clay mineral. Relatively little work has been done on the clay mineralogy of Paleozoic sediments. The studies of Oinuma and Kobayashi (1963) and Nishiyama et al. (1973) showed that kaolinite is rare in such sediments. However, kaolinite-rich red shales have been reported by Igo (1961) from a Carboniferous formation at Fukuji, Gifu Prefecture. These shales overlie limestone disconformably and are considered to have been derived from lateritic materials. Extensive studies on the clay mineralogy of argillaceous rocks of the Cretaceous and Tertiary have been carried out by Aoyagi et al. (1975, 1976). Kaolinite was found to be dominant in argillaceous sediments in brackish and neritic environments and in coalbearing formations.

200

KAOLIN MINERALS

In Japan, there are three major coal-fields, Ishikari in Hokkaido, Joban in northeastern Honshu, and Chikuho, etc. in northern Kyushu. In all, the coal seams are intercalated into the lower part of Paleogene sediments, mainly of the Eocene in Ishikari and Chikuho and the Oligocene in Joban. Mineralogical studies by Kobayashi and Oinuma (1960/61, 1963) and Oinuma and Kobayashi (1966) in Ishikari, and by Mukaiyama et al. (1964) in Chikuho, have shown that the lowermost part of the Eocene sediments in both areas is rich in kaolinite. Kaolinitic fireclays associated with coal in Ishikari, Joban and Chikuho have been described by Takayasu (1953), by Nagasawa et ul. (1969), and by Kodama et al. (1963) and Hoshino and Oishi (1965), respectively. They consist mainly of disordered kaolinite. Minor coal-fields also occur in the Kitakami mountainlands of northeastern Honshu. The Iwate clay mine in one of them is one of the most important refractory clay mines in Japan, and has been studied by Fujii (1970, 1972) and Iijima (1972b). Here, coal-bearing Oligocene sediments overlie the Cretaceous which contains the above-mentioned redbed at its top. Near the base of the Oligocene sediments, there is a bed of flint clay which consists of a compact aggregate of kaolinite sometimes associated with gibbsite. In the lower part of the Oligocene sediments, there are two coal seams each of which is associated with fireclay composed of kaolinite and quartz. These kaolinites are of the disordered type and have the shape of irregular plates. Many sedimentary kaolin deposits of Pliocene age are distributed around Nagoya, and constitute the most productive kaolin-mining area in Japan. Among them, the following are important: the Set0 area (Tanemura, 1963; Shimizu, 1972a) and Sanage-Fujioka area, Aichi Prefecture; the Tajimi-Toki area (Fujii, 1968), Hara area (Nagasawa and Tsuzuki, 1976) and Naegi area (Nagasawa and Kunieda, 1970), Gifu Prefecture; and Shimagahara area, Mie Prefecture. The lowermost part of the Pliocene formations in these areas is composed of lacustrine sediments deposited in many small-scale basins on a basement of granite, Paleozoic rocks, Miocene rocks, etc. The lower part of the lacustrine sediments is composed mainly of quartz sand and “Gaerome” clay, whereas the upper part is composed of “Kibushi” clay and silty clay. Lignite seams and carbonized wood fragments sometimes occur in the upper part. The Gaerome clay is a plastic kaolin clay including coarse quartz grains and occasional feldspar grains. The Kibushi clay is a dark-colored plastic kaolin clay stained by organic substances, and thus resembles the ball clay in England and the United States. The clay fraction of the Gaerome clay has almost the same mineral composition as the Kibushi clay: they are composed mainly of platy disordered kaolinite associated with minor amounts of tubular halloysite and quartz and with occasional illite and smectite. These sediments are considered to have been derived from the weathered rocks of nearby areas and to have been deposited after sorting.

KAOLINITE AND HALLOYSITE

201

5.2.3. Occurrence :post-depositional alteration of pyroclastics The weathering of volcanic ash and pumice to allophane and halloysite has been described in Chapter 2. White clay composed mainly of halloysite is known to have been formed frequently in the deeper portions of pyroclastic deposits by the action of ground water. The deposits at Ina and Yame are examples. Water-laid deposits of volcanic ash or pumice may also be altered to clay. Tazaki (1973) examined the ash-fall deposits beneath Nakaumi, a brackish lake in western Honshu, and showed that they are composed mainly of a 7 A kaolin mineral, illite, and halloysite. She considered the illite to be an alteration product of the vermiculite-chlorite intergrades which are abundant in the corresponding deposits on land. Uno and Takeshi (1971) examined vitric tuffs intercalated in partly freshwater and partly marine Plio-Pleistocene sediments to the south of Osaka, and found that they were weakly altered to smectite. Diagenetic alteration of Miocene tuffs to smectite associated with cristobalite and zeolite has also been described at many localities, but this subject lies beyond the immediate scope of the present Chapter. The author’s group (Nagasawa and Karube, 1975) has studied the mineralogy of clays formed by alteration of a bed of transported pumice intercalated in Pliocene freshwater sediments around Nagoya, and concluded that two kinds of alteration are involved. The first is early diagenetic alteration, by which smectite was formed in some places and kaolin minerals in others. The kaolin minerals thus formed are a mixture of kaolinite and halloysite. The second process was weathering after the sediments were upheaved. This is considered to be due to circulating ground water, and halloysite was formed by it (Nagasawa and Tsuzuki, 1976). Kaolin clays formed by alteration of pumice or tuff beds are known to be intercalated with the Pliocene sedimentary kaolin deposits around Nagoya mentioned above. The Shimmei kaolin in the Tajimi-Toki area (Fujii, 1968) and white clay in the Naegi area (Nagasawa and Kunieda, 1970) (Fig. 5.14) are examples. They are composed of kaolinite and halloysite or of halloysite alone. Vermicular kaolinite macrocrystals have been found in one of the white clay beds in the Naegi area. Nagasawa and Kunieda (1970) considered them to be an alteration product of biotite phenocrysts in the pumice. At the Iwate clay mine, a thin but continuous layer of grey clay composed of kaolinite occurs in a fireclay bed. It is considered to be an alteration product of pyroclastic material (Fuji, 1970)and may correspond to the “tonstein” of Europe. 5.2.4. Chemical composition

Chemical analysis data for kaolinite and halloysite are given in Tables 5.3 and 5.4, respectively. The modes of occurrence of the analyzed samples were as follows: Mikawa mine, a veinlet in a hydrothermal Cu-Pb-Zn vein; Niida, altered tuff around a Kuroko-type anhydrite deposit; Naegi, vermicular macro-

202

KAOLIN MINERALS

TABLE 5.3 Chemical analysis data of kaolinite Si02 Ti02 A1203 Fez03 FeO MnO MgO CaO NazO KzO HzO HzO Total SiOziAIz03

+

Mikawa 45.80 39.55 0.57 0.18 0.14 0.41 0.03 13.92 0.17 100.77 1.97

Niida

Naegi

43.58 0.49 38.82 0.43 tr.

42.68 0.18 35.64 3.20 0.26 0.02 0.14 0.15 0.24 0.21 13.65 4.32 100.70 2.03

0.43 0.25 0.29 0.26 14.34 0.98 99.87 1.90

Mikawa: Mikawa mine, Niigata Prefecture (Nagasawa, 1953). Niida: Drill core, Niida, Odate, Akita Prefecture (Kimbara and Nagata, 1974). Naegi : Kyoritsu-Naegi mine, Nakatsugawa, Gifu Prefecture (Yamada et al., 1949).

TABLE 5.4 Chemical ana!ysis data of halloysite SiOz Ti02 A1203

Fez03 FeO MnO MgO CaO NazO KeO HzO HaO-

+

Iki 38.15 0.05 35.40 2.15 0.05 tr. 0.75 tr. 0.40 0.11 13.42 10.18

P205

SrO Total SiOz/Alz03

100.61 1.83

Iwano 38.14 0.131 34.27 0.92 0.03 0.031 0.081 0.15 0.22 0.19 125.69 0.059 0.001 99.913 1.89

Iki: Iki mine, Iki Island, Nagasaki-Prefecture (Minato, 1969). Iwano: Iwano. Karatsu, Saga Prefecture (Ishibashi, 1974). Shichinohc: Shichinohe, Aomori Prefecture (Sud6 et al., 1951).

Shichinohe 39.58 30.24 1.74

tr.

0.98 11.08 16.60 100.22 2.22

KAOLINITE AND HALLOYSITE

203

crystals in an altered pumice in a Pliocene sedimentary kaolin deposit; Iki mine, hydrothermally altered vitric tuff; Iwano, an amygdale in basalt; and Shichinohe, Pleistocene bedded clay possibly originating from tuff. 5.2.5.

X-ray and electron diflraction

X-ray diffraction diagrams for selected samples of kaolinite and halloysite are shown in Fig. 5.7. As noted by Iwai (1955), there is a wide variation in the structural integrity of Japanese kaolinite. The most ordered variety, triclinic kaolinite with split (111) and (111) reflections, has been reported from the Roseki deposits at the Kurata mine, Yamaguchi Prefecture (Sudo et al., 1954); the Kawaguchi mine, Akita Prefecture (Honda and Shiikawa, 1957); the Roseki deposits at the Goto mine, Goto Islands, Nagasaki Prefecture (Takeshi, 1958); the Mikawa mine, Niigata Prefecture (Nagasawa, 1961); the Akatani iion mine, Niigata Prefecture (Imai et al., 1965); and the Toseki deposits in the Amakusa Islands, Kumamoto Prefecture (Ozaki et al., 1975). Hydrothermal kaolinites are usually ordered, as exemplified by those at the Kampaku mine and Ibusuki (Iwai, 1955), the Hiraki mine (Tanaka et al., 1963), and the Ebara mine (Ueno, 1964), although the (1 1I) and (11I) reflections are not split in them. More disordered varieties have been reported from the Konomai mine (Sudo, 1954b) and the Roseki deposits at Namera and Tsubonouchi, Yamaguchi Prefecture (Takeshi, 1958). At the Mikawa mine, the kaolinite in the altered wall rocks tends to be more disordered than that in the veins (Nagasawa, 1961). At the Seta mine, the kaolinite in the kaolin zone is more disordered than that in the surrounding quartz-kaolin-alunite zone (Komura and Sudo, 1976). Sedimentary kaolinites are of disordered type irrespective of age. Shimizu (1972b) compared the Hinckley crystallinity index of kaolinites from Pliocene sedimentary deposits around Nagoya with that of kaolinites from Oligocene sedimentary deposits at the Twate clay mine. His results indicated that the former falls mostly between 0.0 and 0.6, whereas the latter falls between 0.3 and 0.8. As shown in Fig. 5.7, kaolinite macrocrystals pseudomorphous after biotite are more ordered than ordinary sedimentary kaolinite. Iwai and Kuroda (1961) examined the X-ray diagrams of sedimentary kaolins from around Nagoya, and showed that the basal spacing is 7.14-7.23 and the mean thickness of the crystallites 150-250 A. The latter value is much smaller than that for ordered hydrothermal kaolinite, several hundred A or more (Iwai, 1959; Iizuka and Kobayashi, 1975). Halloysite has a disordered structure characterized by two-dimensional (I&) bands in X-ray diffraction diagrams (Fig. 5.7). Honjo et al. (1954) examined tubular halloysite samples from Hong Kong and other areas outside Japan, by selected-area electron diffraction as well as X-ray diffraction, and revealed that they have a stacking sequence with two-layer periodicity. Later, such two-layer stacking was also found to be valid for tubular halloysites in Japan, viz. halloysites from the Takatama gold mine (Kitamura, 1958), from weathered granite

A

28

(c~K~)

Fig. 5.7. X-ray diffraction diagrams of kaolinite and halloysite (air-dried and unoriented). A, Kaolinite from the Mikawa mine, Niigata Prefecture, hydrothermal; B, kaolinite from the Kyoritsu-Naegi mine, Nakatsugawa, Gifu Prefecture, altered biotite in a pumice bed; C, kaolinite from the Sone mine, Hara, Gifu Prefecture, clay fraction of Gaerorne clay; D, halloysite from Noma, Aichi Prefecture, matrix of sand in the Pleistocene Noma Formation; E, halloysite from Misuzu, Ina, Nagano Prefecture, deep-weathered pumice. Q denotes quartz reflection.

KAOLINITE AND HALLOYSITE

205

at Kakino (Shimizu, 1972a), from weathered granite and sand matrix at various localities (Nagasawa and Miyazaki, 1976), and from Kusatsu (Kohyama et al., 1977). The study by Kohyama et nl. is particularly important since it demonstrated that halloysite has two-layer stacking in the hydrated state. The cell parameters determined by them for the hydrated material are a = 5.14, b = 8.90, c = 20.7 A, p = 99.7'. An example of the selected-area electron diffraction patterns obtained by the present author is given in Fig. 5.8.

Fig. 5.8. Selected-area electron diffraction photograph of halloysite from Morowa, Aichi Prefecture. The scale-line in the accompanying electron micrograph represents 1 ,urn.

Nagasawa (1969) reported variations in the stability of the interlayer water and in the b-dimension of halloysite, the latter arising from the former at least in part. Nagasawa and Miyazaki (1976) examined many halloysite samples of various origins and showed that all were in a fully hydrated state when half-dried at 100% r.h. ; however, the degree of hydration differed from sample to sample when drying was carried out at 56 % r.h. (Fig. 5.9). They further suggested that the stability of the interlayer water may be related to the age of formation of the halloysite; that is, older halloysite tends to have less stable interlayer water. Iwai (1959) showed from line broadening of the (002) reflection that crystallites of three halloysite samples had a thickness of 50-90 A, while Watanabe (1975) showed by analysis of the line profiles of (001) reflections that crystallites of two halloysites from the Shimosueyoshi Loam had a thickness of 30-50 A.

KAOLIN MINERALS

206

D

I

I

6

I

10

I

I

I

14

6

I

I

10

I

I

I

14

6

I

I

10

I

I

14

6

10

14

2 '6 (CuKu)

Fig. 5.9. X-ray diffraction diagrams of halloysite half-dried at 100% r.h. (upper) and dried at 56% r.h. (lower); oriented aggregate. A, Noma, Aichi Prefecture; B, Otaki, Nagano Prefecture; C, Okusa, Komaki, Aichi Prefecture; D, Misuzu, h a , Nagano Prefecture.

5.2.6.

Inpared absorption

Examples of infrared spectra for kaolinite and halloysite are given in Fig. 5.10. The two minerals exhibit similar spectra except that, as noted by Beutelspacher and van der Mare1 (1961) and by Oinuma and Kodama (1964), halloysite shows broader absorptions and does not have the 940 cm-l band. Nagasawa and Miyazaki (1976) demonstrated that the absorbance ratio of the two OHstretching vibration bands, A3700/A3620, is variable (Fig. 5.1 l), and that older halloysite tends to have a larger value for this ratio. They ascribed the larger values to high structural integrity. Kodama and Oinuma (1963) showed that halloysite has an absorption band at 3570 cm-l. Kato (1976), as a result of extensive studies on the infrared spectra of kaolin minerals, concluded that this small absorption (at 3550 cm-l according to him) was characteristic of halloysite. Farmer (1974) considered the absorption to be due to the hydrogen-bonded hydroxyl, and Yariv and Shoval (1975) assigned this to water in the interlayer space. According to the present author's data (Nagasawa and Miyazaki, M published), this band appeared in the spectra of most of halloysites examined and became weak on drying of the samples at 110°C for 2 hr.

KAOLINITE AND HALLOYSITE

207 x102

Fi

.

5.10. Infrared absorption spectra of kaolinite and halloysite. The samples and labeling are asln Fig. 5.7.

Fig. 5.1 1. OH-stretching bands in infrared spectra of halloysite. The samples and labeling are as in Fig. 5.9.

208

KAOLIN MINERALS

5.2.7. Morphology

Kaolinite always has a platy shape with a tendency to show a hexagonal outline. Some halloysites, e.g. that from the Joshin mine, exhibit tubular morphology. However, some other halloysites have spherical shapes, as established by Sudo (1951, 1953) and Sudo and Takahashi (1956). Detailed geological descriptions of most of their samples of spherical halloysite are not available, although they have indicated that these halloysites were alteration products from vitric tuff. The samples consist of rounded grains, sometimes with polygonal outlines and/ or concentric cracks, and elongated crystals often project out from the rounded grains. Examples of spherical halloysite have been reported from weathered volcanic ash and pumice by Nozawa (1953), Morimoto et al. (1957), Kurabayashi and Tsuchiya (1960), Matsui (1960), Ishii and Kondo (1963), etc., as well as by Sudo (1954a, 1956) himself. They are described in Chapter 2. The white clay in the deeper parts of the Quaternary pyroclastics described in Chapter 2 consists of spherical halloysite, as exemplified by the Yame clay (Kinoshita and Muchi, 1954; Sudo and Takahashi, 1956)and the Ina clay (Nagasawa et al., 1969).Spherical halloysite has also been described from altered pumice beds in the Pliocene sedimentary kaolin deposits at Naegi (Nagasawa and Kunieda, 1970) and the hydrothermal deposits at the Iki mine (Nagasawa et al., 1969; Minato and Utada, 1969). Nagasawa and Miyazaki (1976) have shown that the morphology of halloysite is closely related to its genesis. Halloysites formed by alteration of pyroclastics have the shape of balls or scrolls, sometimes associated with short tubes, whereas those formed by weathering of feldspar in granitic rocks and those formed by deep weathering of sands have the shape of long tubes (Fig. 5.12). Hydrothermal halloysites exhibit both types of morphology. Nagasawa and Miyazaki (1976) ascribed this difference in morphology to the mode of formation; that is, replacement for the former and crystallization in free space for the latter. 5.2.8. Distinction between kaolinite and halloysite

Chukhrov and Zvyagin (1966) established halloysite as a distinct mineral species from kaolinite. As shown by Honjo et al. (1954), it has a stacking sequence with a two-layer periodicity in contrast to the one layer of kaolinite. All the halloysites for which two-layer periodicity was established by electron diffraction so far exhibit the long tubular form. Electron diffraction studies of spherical, scroll-shaped, and short tubular halloysites are thus required. As shown by Chukhrov and Zvyagin (1966), the X-ray pattern in the range of 28 = 20-25" (CuKa) is diagnostic, although halloysite does not usually exhibit distinct reflections in this region due to its stacking disorder. Nagasawa and

GENESIS

209

Fig. 5.12. Electron micrographs of halloysite. A, Iki mine, Iki Island, Nagasaki Prefecture, hydrothermal; B, Misuzu, Ina, Nagano Prefecture, deep-weathered pumice; C, Yamaka mine, Nakatsugawa, Gifu Prefecture, altered pumice; D, Okusa, Komaki, Aichi Prefecture, deep-weathered pumice. The scale-lines represent 0.5 pin.

210

KAOLIN MINERALS

Fig. 5.12 (continued). Electron micrographs of halloysite. E, Morowa, Aichi Prefecture, deep-wea-

thcrcd sand matrix; F, Naegi-Kogyo mine, Nakatsugawa, Gifu Prefecture, weathered feldspar in granite. The scale-lines represent 0.5 ,urn.

Miyazaki (1976) concluded that some of their samples of altered pyroclastics and weathered granite are composed of both kaolinite and halloysite on the basis of the presence of two basal reflections, 7 A and 10 A, for materials halfdried at 100% r.h., the presence of weak reflections characteristic of kaolinite in the range of 20 = 20-25" (CuKa), and the presence of platy crystals together with balls, scrolls or long tubes (Fig. 5.13). These three criteria yielded consistent results; that is, samples with the 7 A basal reflection showed kaolinite lines in the range of 20 = 20-25" and contained platy particles. The most convenient method for distinguishing these two minerals may thus be to examine the basal reflection on X-ray diagrams for materials half-dried at 100% r.h., since this is the most sensitive. However, it is possible that the above concordance in results could arise simply from the limited coverage of the samples. In this connection, Brindley and Souza Santos (1966) have reported that some samples show a discordance between morphology and X-ray properties. Sudo et al. (1950) reported that a kaolin mineral from the Zao sulfur mine had an X-ray pattern characteristic of kaolinite but exhibited tubular morphology. Tsuchiya and Kurabayashi (1958) and Kurabayashi and Tsuchiya (1960) described a kaolin mineral with a diffuse basal reflection between 7 and 10 A and a platy morphology with coexistent tubes, in pyroclastic deposits around Tokyo. The basal reflection of their samples was not composed of separate 7 A and 10 A peaks, but consisted of a continuous diffuse reflection ranging from 7 8, to 10 A which, as shown by

3ENESIS

6

10

14

2 8 (GuKa)

Fig. 5.1 3. Electron micrographs and X-ray diffraction diagrams of halloysite associated with kaolinite. The X-ray diagrams were recorded for oriented aggregates half-dried at 100% r.h. Thescalelines in the electron micrographs represent 0.5 pm. A, Naegi-Kogyo mine, Nakatsugawa, Gifu Prefecture, altered pumice; B, Yamaman-Shimmei mine, Toki, Gifu Prefecture, altered tuff; C, KyoritsuNaegi mine, Nakatsugawa, Gifu Prefecture, weathered feldspar in granite.

212

KAOLIN MINERALS

Churchman et al. (1972), may be due to interstratifications of 10 A halloysite and 7 A dehydrated halloysite. In these examples, the X-ray properties appeared to be inconsistent with the morphology, and further investigations on such materials are thus necessary. Infrared absorption and thermal analysis may constitute useful methods for distinguishing between kaolinite and halloysite. As mentioned above, most, although not all, halloysites exhibit the 3550 cm-1 band in infrared spectra. Minato (1965b) has shown that the dehydroxylation temperature on thermogravimetric curves recorded under near-equilibrium conditions is different for kaolinite and halloysite. The slope ratio of the dehydroxylation peak on differential thermal curves has been proposed as a criterion for differentiating between kaolinite and halloysite (Bramao et al., 1952), although the present author’s results for sedimentary kaolin minerals in central Japan indicate that this may not always be so (Nagasawa, 1969). 5.3,

GENESIS

5.3.1. Hydi8otheruMal

Hemley and Jones (1964) classified the mineral assemblages of hydrothermally altered rocks into three types, viz. incipient associations, intermediate associations, and advanced associations, according to the intensity of hydrogen metasomatisni. Although Nagasawa (1961) reported the occurrence of kaolinite as a product of alteration of an intermediate association from the outer envelope of ore veins at the Mikawa mine, the important occurrences of kaolin minerals belong to advanced associations. Kaolin minerals of such associations result from the action of acid hydrothermal solutions which have leachcd out bases from the rocks. As indicated by Iv(iao (1952, 1958, 1968), the most important feature of the hydrothermal kaolin deposits and other kaolin-bearing deposits, e.g. Roseki deposits, silica-alunite deposits and sulfur deposits, is the zonal arrangement of different minerals. Some of these deposits, e.g. the Roseki deposits at the Goto mine, were formed at the relatively high temperatures which accompany igneous intrusions. Some others, e.g. the sulfur deposits, were farmed under shallow volcanic conditions. In spite of this difference in formational conditions, however, zonal distribution of minerals is a common feature of the deposits. In the Roseki deposits of the Goto mine, a diaspore-rich central zone is surrounded by a pyrophyllite-quartz zone, i.e. they have an alumina-rich core (Iwao et al., 1953;Minato and Kato, 1963). Many other Roseki deposits exhibit similar zonal sequences (Takeshi, 1958; Kinosaki, 1963, 1965; Minato, 1965a; Fujii and Inoue, 1971). One example from the Shokozan area is shown above in Fig. 5.1. As seen from the figure, the zonal arrangement in this area is not so regular,

GENESIS

213

a fact which may be explained by formation conditions in which the rising hydrothermal solutions were locally mixed with meteoric water (Katayama, 1969). Differences in oxidation state between the hanging-wall side and the footwall side support this hypothesis. Kinosaki (1965) noted that the zoning in the Fukuyama deposit does not conform with that in other Roseki deposits. Also, Fujii and Inoue (1971), after reviewing the Roseki deposits of the Hokushin district, Nagano Prefecture, concluded that the Bontenyama deposit exhibits reverse zoning, i.e. silicification zone (center)+pyrophyllite zone-weakly altered zone (margin). The zonal sequences of silica-alunite deposits, e.g. Ugusu and Beppu, and volcanic sulfur deposits are similar to that at Bontenyama, i.e. with a central zone of silicification. Examples are shown above in Figs. 5.2. and 5.5. The alteration zones of active geothermal areas are essentially similar to them (Sumi, 1969; Hayashi, 1973). Two kinds of zonation thus exist, one with an alumina-rich core and the other with a silica-rich core. Minato and Kato (1961) undertook alteration experiments by placing rocks in the hot springs of Beppu and Tamagawa. Alteration to opal and halloysite occurred in the Beppu hot spring at a pH of about 3, but alteration only to opal occurred in the Tamagawa hot spring at a pH of 1.0-1.2. A strongly acid solution seems to favor the formation of silica, since the solubility of alumina under such conditions is high. Tsuzuki (1976) constructed solubility diagrams for the A1z03-Si02-Hz0 system, and, based on the diagrams, explained the two kinds of zonal sequences in terms of the difference in acidity of the solutions. A weakly acid solution becomes saturated first with respect to aluminum minerals, since the solubility of these minerals is low. A strongly acid solution, on the other hand, becomes saturated first with respect to silica, since the solubility of aluminum minerals is much higher in it. Consequently, alteration zoning with a silica-rich core is attributed to a strongly acid solution, whereas that with an alumina-rich core is attributed to a weakly acid solution. Differences in the conditions of formation of nacrite, dickite, kaolinite, and halloysite represent an important problem. Nacrite and dickite tend to be formed as fillings in veins or interstices, i.e. by precipitation from solution. When these minerals occur in the altered rocks themselves, dickite tends to be located in the inner part of the kaolin zone, as seen at the Ugusu mine (Uno and Takeshi, 1977), Kasuga mine (Tokunaga, 1954, 1955) and Akatani iron mine (Tmai, 1960), while halloysite tends to be located in the outer part of the kaolin zone, as seen in the Zao sulfur mine (Mukaiyama, 1959). 5.3.2.

Weathering and sedimentary

Three factors appear to control the differential formation of kaolinite and halloysite in weathered rocks. As mentioned above, kaolinjte is abundant in surface soils, whereas halloysite occurs in the saprolites of deeper horizons. The

KAOLIN MINERALS

214

Coarse sand

Altered pumice

5

10

15

28 ( c ~ K ~ )

Fig. 5.14. Columnar sections of the lower part of the sedimentary kaolin deposits at the Yamaka mine, Nakatsugawa, Gifu Prefecture, and X-ray diffraction diagrams of samples taken from this locality, half-dried at 100% r.h.

REFERENCES

21 5

reason for this contrasting mineralogy remains unknown, although it should be noted that the halloysite, and also that occurring in hydrothermally altered rocks and altered pyroclastics, is not usually accompanied by any other clay mineral. The second controlling factor is the original mineral. As pointed out by Sand (1956), feldspars are weathered to halloysite, whereas biotite is weathered to kaolinite. Examples have been given by Shimizu (1972b), and kaolinite macrocrystals pseudomorphous after biotite, have been reported from several localities (Mitsuda, 1960b; Tsuzuki et al., 1968; Nagasawa and Kunieda, 1970; Tazaki and Tazaki, 1975). The third factor is age. The clay fraction of saprolites of present-day weathering belts is composed almost exclusively of halloysite (Shimizu, 1972b). Weathered feldspar in basement granite covered by Pliocene sediments is composed of halloysite and kaolinite, as shown in Fig. 5.6. At the Iwate clay mine, halloysite does not occur in the weathered rocks covered by Oligocene sediments. These facts support the suggestion of Parham (1969a, b) that halloysite is converted to kaolinite with age. Nagasawa and Miyazaki (1976) have also arrived at a similar conclusion based on mineralogical studies of halloysite of various origins. The difference in mineral composition between Pliocene sedimentary kaolin and the underlying weathered granite represents another important problem. As mentioned above, the Pliocene sedimentary kaolin deposits around Nagoya are composed mainly of kaolinite associated with small amounts of halloysite. The basement granite, on the other hand, is composed of halloysite and kaolinite, the relative amounts being variable. As a whole, the weathered granite contains more halloysite than the overlying clays. One example is given in Fig. 5.14. The halloysite in the weathered granite is of tubular shape and much longer and thicker than that in the overlying clays. Nagasawa and Kunieda (1970) considered that transformation of halloysite to kaolinite has occurred during transportation and early diagenesis. The gradual increase in halloysite observed in sediments from the bottom upwards appears to support this view. Shimizu (1972b), however, has given an alternative explanation for the differences in kaolin minerals based on the fact that the surface layer of the present-day wealhering belt is rich in kaolinite, in contrast to the halloysite-rich nature of deeper horizons. He considers that the kaolinite in the surface layer of the Pliocene weathering belt was eroded out to become one component of the Pliocene sediments, leaving the latter richer in kaolinite than the deeper parts of the Pliocene weathering belt which now remains as basement. The present author suspects that both these mechanisms may have operated. REFERENCES Ando, T. (1952) Geol. Suuv. Japan Rept. NO. 141. Aoki, S., Oinuma, K. and Kobayashi, K. (1975) Contributions to CIay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 161.

216

KAOLIN MINERALS

Aomine, S. (1969) The Clays of Japan, Geol. Surv. Japan, 167 Aoyagi, K., Kobayashi, N. and Kazama, T. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 167. Aoyagi, K., Kobayashi, N. and Kazama, T. (1976) Proc. Intern. Clay Conf. Mexico City 1975, 101. Bates, T. F. (1952) Problems of Clay and Laterite Genesis, p. 144, Amer. Inst. Mining Metall. Eng. Beutelspacher, H. and van der Marel, H. W. (1961) Tonindustr.-Zeitung 85, 517, 570. Bramao, L., Cady, J. G., Hendricks, S. B. and Swerdlow, M. (1952) Soil Sci. 73, 273. Brindley, G. W, and Souza Santos, P. de (1966) Proc. Intern. Clay Conf. Jerusalem 1966,1,3. Chukhrov, F. V. and Zvyagin, B. B. (1966) Proc. Intern. Clay Conf. Jerusalem 1966,1, 11. Churchman, G. J., Aldridge, L. P. and Carr, R. M. (1972) Clays Clay Miner. 20, 241. Farmer, V. C. (1974) The Infrared Spectra of Minerals (ed. V . C. Farmer), p. 331, Mineralogical Society. Fujii, N. (1961) Bull. Geol. Surv. J a p n 12, 647. Fujii, N. (1962) Bull. Geol. Surv. Japan 13, 231. Fujii, N. (1968) Ceol. Surv. Japan Rept. No. 230. Fujii, N. (1970) J. Geol. SOC.Japan 76, 623. Fujii, N. and Inoue, H. (1971) Mining Geol. 21, 407. Fujii, N. and Yasuda, T. (1971) Bull. Geol. Surv. Japan 22, 593. Fujii, N. (1972) Kaolin Symposium, 1972 Intern. Clay Conf., 17. Fujii, N. (1976) The 7th Symposium on Genesis of Kaolin, 1. Fujiwara, T. and Kujirai, S. (1972) Mining Geol. 22, 213. Hayashi, H. (1961) J . Miner. Soc. Japan 5 , 101. Hayashi, M. (1973) J. Japan Geotherm. Energy Assoc. 10, (3), 9. Hemley, J. J. and Jones, W. R. (1964) Econ. Geol. 58, 538. Honda, S. and Shiikawa, M. (1957) Rept. Inst. Develop. Underground Resources Akiia Univ. 18,l. Honda, S., Hayashi, A. and Shimazaki, K. (1963) Industrid Mineral Resources in the Tohoku District, vol. 3, p. 76. Honda, S., Miura, T., Ohira, Y . and Tamanoi, M. (1964) Industrial Mineral Resources in the Tokoku District, vol. 4, p. 87. Honjo, G., Kitamura, N. and Mihama, K . (1954) Clay Miner. Bull. 2,133. Hoshino, Y. and Oishi, M. (1965) Advances in Clay Science, vol. 5, p. 241, Gihodo. Hukuo, K. and Kutina, S. (1960) Advances in Clay Science, vol. 2, p. 101, Gihodo. Ichiko, T. (1971) J. Clay Sci.SOC.Japan, 11, 1. Japan, 67, 261. Igo, H . (1961) J. Geol. SOC. Iijima, A. (1972a) Mining Geol. 22, 1 . Iijima, A. (1972b) J. Fac. Sci. Univ. Tokyo Sec. 11, 18, 325. Iizuka, M. and Kobayashi, K. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 23. Imai, N. (1960) J. Fac. Sci. Niigata Univ. Ser. II,3,205. Imai, N., Otsuka, R. and Watanabe, K . (1965) J. Clay Sci. SOC.Japan 4, 113. Ishibashi, K. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 69, 255. Ishii, J. and Kondo, Y . (1963) Advances in Clay Science, Vol. 4, p. 193, Gihodo. Isobe, K., Hoshina, K. and Sugaki, A. (1967) Mining Geol. 17, 22. Iwai, S., Takeshi, H. and Ossaka, J (1949) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 33, 169. Iwai, S. (1955) Miner. J. 1, 233. Iwai, S. (1959) Advances in Clay Science, vol. 1, p. 28, Gihodo. Iwai, S. and Kuroda, Y . (1961) Advances in Clay Science, vol. 3, p. 160, Gihodo. Iwamoto, S. (1963) Geof. Rept. Hiroshima Univ. 12, 73. Iwao, S. (1949) Geol. Surv. Japan Rept. No. 130. Iwao, S. (1952) Mining Geol. 2, 120. Iwao, S., Hamachi, T., Yamada, M. and Inoue, H . (1953) Bull. Geol. Surv. Japan 4, 81. Iwao, S. (1958), Sci. Pap. Coll. Gen. Educ. Univ. Tokyo 8, 93. Iwao, S. (1962) Japan. J. Geol. Geograph. 33, 131. Iwao, S. (1968) Proc. 23rd Intern. Geol. Congr. Prague, 14, 107. Iwao, S. (1970) Volcanism and Ore Genesis (ed. T. Tatsumi), p. 267, Univ. Tokyo Press. Japan 12, 51. Kakitani, S. and Kono, T. (1972) J. Clay Sci. SOC. Katayama, N. (1969) Mining Geol. 19, 31.

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