J. Japan. Assoc. Min. Petr. Econ. Geol. 69, 275-284, 1974

NESQUEHONITE FROM YOSHIKAWA, AICHI PREFECTURE,

JAPAN: OCCURRENCE AND THERMAL BEHAVIOUR

JUJIN SUZUKI* and MASAHIRO ITO**

* Department of Earth Sciences , Aichi University of Education, Xaviya. ** Laboratory of Earth Sciences , Department of General Education, Nagoya University, Nagoya.

Nesquehonite, MgCO,•E3H2O, from Yoshikawa, Aichi Prefecture, the first occurrence in Japan is described. It is found as columnar aggregates covering the encrustment of "yoshikawaite" on the weathered surface of the serpentinite. The X-ray diffraction

pattern and the optical properties are identical to those of the previous data. The nesquehonite is thermally decomposed lastly to periclase through the three inter mediate phases, that is, the dehydrate phase (80-200•Ž), the amorphous phase (210-270•Ž) and the decarbonate phase (280-480•Ž). Periclase is produced at 370•Ž. A few absorp tion bands characteristic of the decarbonate phase are already found in the infrared spectrum of the amorphous phase. DTA curve for nesquehonite shows six endotherms with maxima at 132, 176, 216, 420, 507 and 526•Ž, respectively, and an exotherm at 499•Ž. The first three endotherms are attributed to the removal of H2O, and the others to that of CO2. The exothermic reaction is considered to be coupled with the fifth endothermic one.

1. INTRODUCTION magnesite and trace of monohydrocalcite, calcite and aragonite (Fischbeck and Muller, Nesquehonite, MgCO3•E3H2O, one of the 1971), (2) in serpentinite, (3) in coal mine simple magnesium carbonate hydrate mine (Winchell and Winchell, 1951) and so on. rals, from Yoshikawa, Aichi Prefecture was It was also found even in the carbonate found for the first time in Japan. The X- scales in the air scrubber of an air-condi ray diffraction, DTA curves and optical tioning plant, associated with hydrocalcite properties are identified with those of the and calcite (Marschner, 1969). A mixture nesquehonite reported by other workers. of nesquehonite and aragonite was reported It occurs closely associated with an unusual to be formed from the sea-water by the magnesium carbonate hydrate mineral, Mg5 vapour phase diffusion technique (Towe •@(CO3)4(OH)2.8H2O, *** which covers the ser and Malone, 1970). pentinite body as the encrustment, having Some mineralogical and crystallographi a characteristically long spacing of 33.2 A cal studies of nesquehonite have been re (Suzuki and Ito, 1973). Other natural oc currences of nesquehonite are, for example, ported, most of which were done for synthe sized specimens. Stephan and Macgillavry (1) in cauliflower-like rough crust on the small wall of upper Juarssic dolostone cave (1972) determined the crystal structure of

of West Germany, admixed with hydro nesquehonite synthesized by the method of

*** Application for an approval of the name, "yoshikawaite," is pending. (Manuscript received, April 15, 1974) 276 J. Suzuki and M. Ito

Menzel and Bruckner. Since it has some The serpentinite body contains some noticeable behaviour indicating the change amounts of brucite and is conspicuously into periclase due to thermal decomposition, carbonate-hydrated, forming hydrotalcite keen attention has been paid. It passes group-mineral, hydromagnesite and artinite. through the stages accompanied by a few Aragonite and hydromagnesite coexist also intermediate phases (Morandi, 1969; Iwai as vein-fillings in the serpentinite. As re et al., 1969). ported in the previous paper (Suzuki and In this paper, the occurrence and the Ito, 1973), the encrustment of "yoshikawa thermal behaviour of nesquehonite from ite" is an evaporation product, on the sur Yoshikawa will be presented in detail based face of the cutting cliff, from the ground on the characteristics in X-ray diffraction water near the surface which dissolves patterns, DTA-TG curves and infrared brucite, hydrotalcite group-mineral and the spectra. related minerals. This unusual "yoshikawa The optical properties of nesquehonite ite" is slightly soluble even in distilled water are as follows: ƒ¿<1.448, ƒÀ=1.504, ƒÁ= and is more soluble in rain water. Judging 1.528; ƒÁ-ƒ¿>0.080, ƒÁ-ƒÀ=0.024. It is colour from the occurrences, nesquehonite is also less and shows nearly straight extinction considered to be an evaporation product on with positive elongation. the surface of "yoshikawaite" mainly from rain water which dissolves the latter mine 2. MODE OF OCCURRENCE ral. Brucite, hydrotalcite group-mineral,

Nesquehonite is nearly colourless and hydromagnesite and other magnesium car transparent, and slender column-like crystals bonate hydrate minerals are soluble slightly

(Fig. 1). It occurs as columnar aggregates in the water with dissolved CO2. Nesque growing perpendicular to the surface of the honite is observed to be formed by evapora encrustment of "yoshikawaite" covering tion from such a solution at room tempera the serpentinite body (Fig. 2). ture. However, in Yoshikawa nesquehonite

Fig. 1. Scanning electron microphotograph of Fig. 2. Nesquehonite covering the encrustments nesquehonite. of "yoshikawaite." Nesquehonite from Yoshikawa, Aichi Prefecture, Japan: Occurrence and thermal behaviour 277

Table 1. X-ray powder diffraction data for nesquehonite from Yoshikawa, Aichi Prefecture, Japan.

* Left alone at room temperature for three months after heated to 520•Ž. 278 J. Suzuki and M. Ito

has the strongest reflection peak for 16.9•‹

(2Į). Above this temperature the peak decreases in height gradually and complete

ly disappears at least at 230•Ž, showing the

formation of amorphous phase (the second

phase). The dehydrate phase has generally broad peaks, whose reflection lines are most

ly inherited from those of nesquehonite,

and the lattice is slightly contracted with

rising temperature. The third is the decar

bonate phase and will be discussed in later

section. It appears at 280•Ž showing very

sharp lines, and disappears suddenly at 490•Ž

. Periclase, the fourth phase, begins to

appear at 370•Ž and increases gradually in

crystallinity with rising temperature, follow

ed by slight contraction of the lattice.

However, magnesite is not recognized

throughout the decomposition process.

The periclase formed from nesquehonite

by heating up to 520•Ž was left alone in Fig. 3. X-ray diffraction patterns for nesquehonite air at room temperature for about three and its thermal decomposition products. months, whose diffraction datum is given CuKƒ¿ radiation was used for 2ƒÆ. in the last column of Table 1. A few new

occurs in association with only "yoshikawa reflection lines appear together with those ite" and not with brucite and any other of periclase. The reproduced phase shows carbonate hydrate minerals. the d-spacing similar to that of brucite.

3. X-RAY DATA 4. THERMAL ANALYSIS

CuKƒ¿ radiation was used. The thermal Simultaneous DTA and TG curves of

effects on the whole X-ray diffraction pat nesquehonite are shown in Fig. 4, together

terns of nesquehonite are shown in Table 1 with that of the periclase from the 520•Ž

and Fig. 3. It is heated in air for about 10 heated nesquehonite, mentioned in the

to 20 minutes at each 10 or 20•Ž interval above section. The heating rate is 10•Ž per

between 40 and 520•Ž on the Pt-heating minute in air. There are six endothermic

stage of the high temperature X-ray diffrac reactions, 132, 176, 216, 420, 507 and 526•Ž,

tion apparatus. All measurements were and an exothermic reaction at 499•Ž. The

made for the specimens cooled to room endotherm at 486•Ž is considered to be due

temperature after heating. Four decompos to the coupling of the endothermic reaction

ed phases are recognized with rising tempe at 507•Ž and the very rapid exothermic

rature. The first is the dehydrate phase reaction at 499•Ž.

which appears at 80•Ž. At about 100•Ž it TG curve shows the continuous weight Nesquehonite from Yoshikawa, Aichi Prefecture, J apan: Occurrence and thermal behaviour 279

s loss s untill the last reaction is completed.

Judging from the first appearance of peri clase in the X-ray pattern at 370•Ž, the

three endotherms at lower temperature re

gion are related to the escape of H2O, and the other three at higher temperature region

to the escape of CO2. If the weight loss

for each endothermic reaction is estimated

from the TG curve for each temperature

range, shown on the DTA curve of Fig. 4,

the variations in the chemical compositions

of the residuals through each reaction with

rising temperature may be suggested as

shown in Table 2. There is very slight

weight loss towards higher temperature

even after the last endothermic reaction is

finished at about 550•Ž. It attains about

0.03 mole ratio of CO2 at 1000•Ž. This

weight loss may be regarded as an observa

tional error. However, it is significant to

note that the periclase from nesquehonite

heated even up to 1000•Ž is also chemically active and is found to adsorb some amounts

of H2O and CO2 at room temperature. The Fig. 4. DTA-TG patterns: A, nesquehonite; B, periclase from the 520•Ž-heated nesqu periclase from the 520•Ž-heated nesqu ehonite, left alone in air at room temper ehonite. The heating rate is 10•Ž/min. ature for about three months, shows a

Table 2. The thermal decomposition products of characteristic DTA-TG curve as shown in nesquehonite at various temperatures Fig. 4. There occur two endotherms at between room temperature and 1000•Ž in air. The heating rate 10•Ž per 102 and 385•Ž, respectively. The former minute. reaction is caused by the escape of HO

and the latter by the escape of CO2. The

total weight loss is 28.6%, made up as

follows: 7.8% of H2O and 20.8% of CO2,

respectively.

A few DTA curves by the various heat

ing rates have been reported. The pattern

in this paper is rather similar to that by

Morandi (1969), except a few differences.

He showed the endotherms at 160, 190, 220,

Total seight loss in 'TG curve: 70.53 430 and 525•Ž, and the exotherm at 515•Ž. 1) ssorptnus phase.

21 decarbonate phase and periclase in X-ray pattern. The first two endotherms are higher than 3) periclase in X-ray pattern those in this paper. The exotherm in his 280 J. Suzuki and M. Ito

paper is conspicuously strong unlike those range of the frequencies. reported by the other workers. All endo (A) 4000 to 2000cm-1 therms below 300•Ž are generally attributed A sharp and strong absorption band at to the escape of H2O. Beck (1950) and 3540cm-1 for the non-treated nesquehonite

Morandi (1969) assigned the endotherm at is due to the vibration of O-H stretching about 430•Ž to the escape of OH. However, and disappears at 60•Ž. A sharp band at judging from the detailed investigation of 3550cm-1 is observed at 60•Ž and as a the TG curve, it may be safe to attribute shoulder at 100•Ž. Very sharp bands at the endotherm to the escape of CO2. This 3680cm-1 are found for the samples heated is also supported by the appearance of at 440 and 500•Ž. The absorption is clearly periclase on X-ray diffraction patterns even caused by the water adsorbed by the peri

at 370•Ž. Therefore, the third phase is clase formed from nesquehonite. A sharp considered to be the decarbonate. The

endotherm around 520•Ž has been attribut

ed to the escape of CO2. The nesquehonite

from Yoshikawa shows two coupled endo

therms at 507 and 526•Ž, respectively, both

of which are from the escape of CO2. But

the former reaction is very complicated, as

it is coupled with the exothermic one.

After all, nesquehonite from this area is

thermally decomposed to periclase through

the three steps of the escape of H2O and

those of CO, respectively.

5. INFRARED ABSORPTION SPECTRA

The infrared spectra of nesquehonite

and its heated samples are shown in Fig. 5

and the frequencies of the absorption bands

in Table 3. The heated ones are the same

as those used for the X-ray diffraction.

All measurements were made at room

temperature by the KBr disc technique.

The two extra bands at 3670 and 3620cm-1

indicated by asterisks for non-treated nes

quehonite are due to the admixed chryso tile and "yoshikawaite," respectively. Since

purified samples were used for heating ex

periment, the two extra bands do not appear on the other spectra. Fig. 5. Infrared absorption spectra of nesquehonite Characteristic changes in the thermal and the minerals heated at various temper decomposition will be described for each atures. Nesquehonite from Yoshikawa, Aichi Prefecture, Japan: Occurrence and thermal behaviour 281

Table 3. Infrared absorption data for nesquehonite from Yoshikawa, Aichi Prefecture.

* Chrysotile, ** "Yoshikawaite"

band at 2350cm-1 and the shoulder at 2380 buted to the water adsorbed into KBr from cm-1 appear at least at 250•Ž, increasing in the decarbonate phase rather than from intensity above this temperature, and dis periclase, although this phase does not show appear below 500•Ž. Since this temperature any signs of adsorption of water in the X- range is assigned to the amorphous phase ray diffraction pattern. and the decarbonate phase, the two absorp (B) 2000 to 1300cm-1 tion bands are derived from newly formed Four distinct absorption bands at 1639, bonding in the decarbonate phase. It is 1513, 1474 and 1418cm-1 are observed at noted that this new bonding is already form room temperature. All bands become diffus ed in the amorphous phase at 250•Ž. ed with rising temperature. A band by H-

Furthermore, an indication of this bonding O-H bending appears at 1639cm,-1 and is seen even at 180•Ž as a weak and broad disappears at least at 100•Ž. The band at band. The intensity of this band increases 1474cm-1 is not distinctly observed at 60•Ž. at 290 to 350•Ž, though the frequency is The other absorption bands at 1513 and somewhat less by about 15cm.-1 Two 1418cm-1 become broad with rising tempe sharp but weak absorptions at 2930 and rature. Newly formed bands are observed

2850cm-1 may probably belong to the decar at 1587cm-1 at 60•Ž and 1385cm-1 at bonate phase, since no absorption is found 500•Ž. The latter is a diagnostic one for in the same frequency region for the sample the periclase from the heated nesquehonite, heated at 500•Ž. Or, they might be attri in which a large amount of H2O and CO2 282 J. Suzuki and M. Ito

is adsorbed. (D) 800 to 400cm-1

White (1971) showed three bands at The absorption spectra in this frequen

1518, 1470 and 1415cm-1 to be caused by cy region change rapidly with rising tempe the absorption of C03- stretching. How rature. All bands become broad even at ever, it is interesting to note that all bands 60•Ž. The dehydrate phase and the decar become gradually diffused with rising tempe bonate phase are characterized by the bands rature, in spite of the fact that the decar at 630 and 660cm-1, respectively. The bonate phase shows higher crystallinity in periclase from the heated nesquehonite does X-ray diffraction patterns. not show any distinguishable absorption spec (C) 1300 to 800cm-1 trum. The band at 797cm-1 is also com

The dehydrate phase, the decarbonate patible with that of "yoshikawaite." But, phase and the periclase from the heated judging from the same reason as mentioned nesquehonite are characterized by the broad above, it is also ascribed to the absorption bands at 980, 1094 and 1075cm-1, respec by nesquehonite. tively. The absorption at 1095cm-1 pro bably by CO23- stretching in thermally non 6. DISCUSSIONS treated nesquehonite is stronger at 100•Ž Some intermediate products through than those below this temperature, and then the thermal decomposition of nesquehonite become broad with rising temperature. The have been reported by many workers. But bands at 948 and 878cm-1 disappear com all of these are not always crystalline by X- pletely at 60 and 180•Ž, respectively. The ray diffraction. As mentioned above, three latter band may correspond to that of "yoshikawaite crystalline phases and an amorphous one are ." However, it should be identified. A schematic representation of attributed to nesquehonite, because the "yoshikawaite" heated to 180•Ž shows the the thermal decomposition of this mineral

may be compiled as in Fig. 6. bands as strong as that at room tempera ture. The sharp band at 849cm-1 by CO23- The thermal decomposition of the bending becomes broad with rising tempera sample heated for the X-ray diffraction is ture up to 440•Ž. Another characteristic considered to proceed rapidly enough so as band of the periclase from the heated nes to form the metastable phases within ten quehonite is observed at 860cm-1. to twenty minutes at various temperatures,

Fig. 6. Schematic diagram of the thermal decomposition of nesquehonite. v & •¢ : endothermic and exothermic maxima, respectively. o : temperature on DTA curve. ESQ.: nesquehon ite. Nesquehonite from Yoshikawa, Aichi Prefecture, Japan: Occurrence and thermal behaviour 283

since even the sample held for more than 24 phase between 410 and 440•Ž shows the hours shows no significant change in the X- strongest peak heights of the X-ray reflec ray pattern. The samples for DTA-TG tion lines, though the subsequent phase, weigh about 15 to 20mg, but those for the periclase, is already formed in some X-ray analyses about 1 g. In both thermal amounts. The decrease in intensity of the

treatments, the heating rates are approxi absorption at 2350cm-1 in the sample

mately the same. Therefore, the "holding" heated to 440•Ž is caused by the decrease

effect on the larger amount of sample is in quantity due to its decomposition. It is

considered to correspond to the continuous completely decomposed by heating from 480

uprising of temperature for the less amount to 490•Ž without any diffused X-ray pat

of sample for DTA-TG with the constant terns. This temperature range corresponds

rate of 10•Ž per minute. to the exothermic reaction of the maximum

The chemical composition of the dehy at 499•Ž. Therefore, the decomposition is

drate phase changes gradually from MgCO3 completed just before this exothermic reac

3H2O to MgCO3.0.77H20 with rising tempe tion starts. The chemical composition of

rature. However, three distinguishable this phase is about MgO.0.44 CO2 at 499•Ž.

endotherms with continuous weight loss Only periclase is observed in the X-ray

are found on the DTA curve. Judging from diffraction patterns above 490•Ž, which

the X-ray patterns, this phase is related show, however, broad reflection lines. It is

to the first two endotherms. As all the interesting to note that some amounts of reflection lines become broad above 120•Ž, CO2 are contained in the periclase, and is

the thermal condition below this tempera released gradually with rising temperature

ture corresponds probably to the endother up to 550•Ž. Judging from the two distinct

mic reaction of the maximum at 132•Ž. endotherms at 507 and 526•Ž, the CO2 may

Then, the broad peaks for each pattern be loosely joined to very fine-grained and less crystalline periclase by two somewhat gradually disappear with rising temperature through the endotherm at 176•Ž, and the different ways. Explanations of the exothermic reac patterns of the amorphous phase appears. The amorphous phase contains some tion have been discussed by many workers.

amounts of H20, that is, 0.77 mole which The magnesium carbonate hydrate minerals

is equal to 25.7% of total H2O. It is are generally characterized by this exotherm

continuously lost probably up to 351•Ž, and the subsequent endotherm. It is re

through the endotherm at 216•Ž. However ported that this exotherm might be caused

the decarbonate phase appears already at by the crystallization of periclase with a

280•Ž in the X-ray pattern. As strikingly question mark added in the table (Beck,

shown in the infrared spectra, the absorp 1950). Morandi (1969) concluded that it is tion bands characterized by this phase are attributed to the formation of magnesite,

already observed even in the amorphous based on the DTA data under CO, condi tion. On the other hand, Iwai et al. (1969) phase at 250•Ž. Therefore, the formation of new chemical bonds suggestive of the suggested the abrupt contraction of the

decarbonate phase is distinctly proceeding lattice of periclase through the process of

in the amorphous phase. The decarbonate increasing in crystallinity around 500•Ž. As 284 J. Suzuki and M. Ito already mentioned above, magnesite is not REFERENCES recognized in air, and the lattice of periclase Beck, C.W. (1950), Differential thermal analysis also contracts gradually with rising tempe- curves of carbonate minerals. Am. Mineral., 35, 985-1013. rature. However, this exothermic reaction Fischbeck, R. and Miiller, G. (1971), Monohydrocal- is drastic and even explosive, especially in cite, hydromagnesite, nesquehonite, dolomite, hydromagnesite and "yoshikawaite." It aragonite, and calcite in speleotherms of the Frankische Schweiz, West Germany, Contr. might have been caused by some other reac- Miner. Petrol., 33, 87-92. tions which can release a great amount of Iwai, S., Murotani, H., Morikawa, H. and Aoki, H. energy within a short time. Further study (1969), Thermal decomposition of MgCO2.3H2O. on this topic will be reported in the near (in Japanese with English abstract), Yogyo- Kyokai-Shi, 77, 25-31. future. Marschner, H. (1969), Hydrocalcite (CaCO2•H20) and nesquehonite (MgCO2.3H20) in carbonate scales. Science, 165, 1119-1121. ACKNOWLEDGMENTS Morandi, N. (1969), La dissociazione termica dell 'idro -magnesite e della nesquehonite. Miner. Sincere appreciation is extended to Dr. Petrogr. Acta, 15, 93-108. K. Sakurai for giving a private communica- Stephan, G.W. and Macgillavry, C.H. (1972), The crystal structure of nesquehonite, MgCO3. tion about the informations on some magne- 3H20. Acta Cryst., B28, 1031-1033. sium carbonate hydrate minerals from the Suzuki, J. and Ito, M. (1973), A new magnesium carbonate hydrate mineral, Mg. (COZ)4(OH)2. serpentinites in Japan. Thanks are due to 811,0, from Yoshikawa, Aichi Prefecture, Professor I. Sunagawa of Tohoku Univer- Japan. J. Japan. Assoc. Min. Petr. Econ. sity for kind advice, Dr. H. Nakata of the Geol., 68, 353-361. Department of Chemistry, Aichi University Towe, K.M. and Malone, P.G. (1970), Precipitation of carbonate phase from seawater. Nature, of Education, and Dr. S. Matsuura of the 226, 348-349. Department of General Education, Nagoya White, W.B. (1971), Infrared characterization of water and hydroxyl ion in the basic magne- University for kindly assisting in the inter- sium carbonate minerals. Am. Mineral., 56, pretation of infrared spectra, and Mrs. 46-53. Sugimoto for translation of Morandi's paper Winchell, A.N. and Winchell, H. (1951), Elements into English. of optical mineralogy, part II. 4th ed., John Wiley & Sons, inc., New York.

愛 知 県 吉 川 産nesquehonite 鈴木 重人,伊 藤 正裕

Nesquehonite(MgCO3・3H2O)が,含 ブ ル ー サ イ 卜蛇紋岩 の風 化 面 を 覆 う"yhikawaite"の 表 面 か ら発見 され, X線 回 折 お よび 光軸 性 質 に基 づ き同 定 され た 。 無 色透 明 の柱 状 結 晶 を な す 。 本鉱 物 は,温 度 の 上昇に と もな い,脱 水 相,非 晶 質 相 お よび脱 炭 酸 相 を 経 てぺ リク レ ー スへ 分 解 す る。非 晶 質相 のIRパ タ ー ンに は す で に脱 炭 酸 相 を特 徴 づ け る吸 収 帯 が あ る。 ま た, DTAで は132, 176, 216, 420, 507, 526℃ に 吸 熱, 499℃ に 発 熱 を示 す 。 こ の発 熱 反 応 は,含 水 マ グ ネ シ ウ ム炭 酸 塩 鉱物 群 に共 通 し て お り,こ の 原 因 に つ い て 言 及 した 。