(Fischbeck and Muller, 1971), (2) in Serpentinite, (3) in Coal Mi
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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•‹ (2ƒÆ). 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.