1960 THE AMERICAN MINERALOGIST, VOL 45, SEPTE\'IBER-OCTOBER' AN INTERSTRATIFIED MIXTURE OF MICA CLAY MINERALS Susuuu SnrnooeaNp Tosnro Suoo,Tokyo Uniaersityof Etlucation,T okYo,J aPan. Assrn.{ct INrtouucuoN found almost free from impurities. Thus such mineralsare not so Iare as ap- we have hitherto anticipated, and the present mineral is considered propriate for the description of its mineralogical and crystallographic properties. MopB ol OccuRRENCE 1O7O S. SHIMODA AND 7.. SUDO complexmineral yonago associations.The mine now being consideredis one of the important pyrophyllite-diaspore depositsin Japan. The area near the ore deposit consists of fine grained sandstoneand shaleintruded by porphyrite and andesitedykes. A[ of theserocks are covered by a lava flow. The ore deposit occursalong the boundary zone between the porphyrite and andesitedykes repracingboth of theserocks. The ore bodies consist of diaspore,cray minerals, quartz and pyrite. Diaspore occurs as compact or powdery massesmostly cemented by pyrophyllite. About eighty specimenswere coilectedin the area inciuding the ore deposit, and the amounts of the minerals in each specimenwere esti- mated by r-ray analysesusing an internal standard of fluorite. standard curves were made using pure clay mineralsfrom the other locaiities.The confirmed mineralsare diaspore,pyrophyllite, quartz,sericite, kaoiinite, halloysite, montmorillonite, and pyrite. By plotting the result of the qualitative estimationsof these minerals except pyrite, zonar distribu- tions were confirmed particularly with regard to ttre distributions of diaspore,pyrophyllite, and kaolin minerals.The center of the zonal dis- tribution was confirmed in two difierent places; in both of which the zonal distributions were found to be (diaspore and pyrophyllite)_ (kaolin minerals)-( quaftz), going progressively u*uy fro- ih" ."rrr".. The mineral nameswritten in parenthesesare thoseof the principal min- erals in each zone. The boundariesbetween these zonesu.. roi sharp, but gradually gradeinto one another. Diasporeis rather more dominant in the central area than pyrophyilite, but in most casesboth of these minerals occur mixed with each other in various proportions. pyrite crystals are dominant in the kaolin mineral zone.Sericite occurs in small amounts throughout thesezones, but tendsto be dominant in the silicious zone. Montmorillonite occurslocaily in the siliciousand kaolin mineral zones. clay minerals showinglarge spacingsin their powder diffraction data are frequently noted: Type I (specimens 11 and 63): This mineral showsa 26 A spacingand will be discussedin detail in this report. rt occurswidely in the ore area, particularly dominantly in the pyrophyllite-diaspor",on",frequently as vein-shapedmasses in the pyrophyllite bodies. Type (specimen II 1): This mineral alsoshows a spacingof about 26 A and occurs only in the kaorinitezone. Because of difficulty.-inobtaining a pure sample,we could not ascertainits detailedmineralogical properties, but it seemsto agree with rectorite (Bradley, 1950), or the 26 A.tay mineral found from the Honami pyrophyllite deposit,Nagano prefecture (Kodama, 1958). Type rrl (specimen 38): This is found rarely in the siliciouszone as INTERSTRATIFIEDMIXTURE OF MICA CLAY MINERALS 1O7I thin crusts covering siliciousrock fragments. The siliciousarea usually shows brecciated structures consistingof siliciousrock fragments. Be- causeof difficulty in obtaining a pure sample,we could not determineits detailed mineralogicaland properties, but it seemsto agree with the aluminian mixedJayer mineral recently found from the Kamikita mine, Aomori Prefecture(Sudo and Kodama,1957). 26 A Cuv MrNnn.q,r(Tvro I) Macroscopicproperties: This mineral occursas white compact masses rvith greasyluster resemblingthe pyrophyilite masses,and is associated with the pyrophyllite-diasporezone. We could not determineits detailed mode of occurrence,but someof it surely occursas vein-shapedmasses in pyrophyllite bodies. By r-ray testing,we found specimensalmost free from impurities, and obtained the following data from the crude specimens.Their lc-rayre- flections consistof the clear and sharp 26 A reflection and its higher orders except the weak 4.27h reflection which is probably due to a small amount of impurity. On close examination oI the 26 A reflection under various experimentalconditions as studiedwith a slow scanningspeed, or using the internal standardof a-stearicacid, the spacingappears to vary slightly from specimento specimen.Basal spacingsobtained from nine referencespecimens and also the mean valuesof eachset of basal reflec- tions are given in Table 1. From eachof thesemean value the 001 spac- ings werecalculated, and 26.1* 1 A was obtainedas the final meanvalue. Tesr-B 1. Beslr- SpecrNcs oF TIrE 26A CI,Iv-MTNERAL lRoM rnr YoNlco MrNn o 001 I d I 001 zasA 01s 44m zo air 60s 002 128 52vs 47s 125 50s 005 512 25s 27 vs 506 34s 008 324 J0s 40 vs 325 34m 00.10 257 26s ,12vs 2.57 35s 8 Mean d I d 001 zt-oL 50m 27 6A zt.aL zt oL oo2 1,29 25.8 005 510 25.5 008 3.25 260 00.10 2.57 25.7 Mean 26.111A IO72 S, SHIMODA AND T. SUDO Worthy of notice is that the 26 A reflectionis usually accompaniedby a tailed reflectionon its small angleside, but we could not find reflections attributable to superstructuresof the 26 A ore. Effects of heat (Table 2): The specimenanalysed by r-ray diffraction washeated at eachof the temperatures300o C.,500o C., 700oC., g00oC., and 1000oc. for one hour and sealedinto a glasstube immediately after cooling,and kept in the sealedglass tube until it was studied by r-rays. rn the specimenheated at 300oc. for one hour, the 26 A reflectionwas just visible, and its higher order reflectionswere somewhat weakened. The 13 A reflectionshifted to a 10.3A reflection,and the 5.10 A reflec- TasLE 2. X-Rny Drnln,qcrron Der,l ron rnn Arn-Dnvro 26 A Cr,lv MtNnnar (CuKa, 1.5418A) r- Room temD .300'c 700'c 900'c. 1000"c I dlr dlI zo.z,&]+o'" z+.sAI s"t rS,+A 130 33 vs rr sA 5b rr.eA 7b 12b r09 5D 104 8b 103 103A 9.9 OD 10.0 10b 93 .JD 510 lo s 8m 507 5D 504 9s 507 10s s09 3m 4.48 19s 20 vs 453 4 51 38 vs 451 42 vs 4.50 8m 4.27 10 vs 21 vs 4 31, 3s 4.27 7vs 387 4vb 3.92 6b 380 6b 3vb 355 JD 340 8vb 335 10m 27 vs 3.35 30s 3.29 8s 7vs 327 9vs 325 310 4b 3 .03 2vb 3.08 4b 284 2vb 288 JO 2.?0 2b 2.56 15s ?<o 9m 2.59 t0b 259 11m 251 JVD 252 5D 2.54 3vb 2.49 JD 2.49 5D 248 3vs 249 4b 244 4b 242 .J VD 241 3vb 2.41 4b 239 4b 4b 2.25 3b 226 JVO 226 6m .JD 2.19 3vb 2.13 JVO 214 3b 213 4vs 2.13 2b 2vb 2.03 2b 201 4vb 2 01, JD 1.99 JD 179 4b .tD 172 .t vD JD 1.69 3b 3vb 1.67 3vb JD JD 1.65 155 5s 1.50 9m 4b w: very sharp. s: sharp. m; medium b: broad. vb: very broad. IN'T'ERSTRAT'IFIEDMIXT'TJIIE OF MICA CLAY ['IINERAL'S 1073 rion was replacetlby a 5.01A reflet.tio..fhe 3.27 A reflectionbccame broader, and its spacing was replaced by a slightly larger spacing of 3.29 A. In the specimenheated at 500oC., the 26 A reflectionwas still just visible.Its higher order reflectionsbecame weaker than in the caseof the specimenheated at 300oC. The 3.27 h reflectionwas replacedby a broad reflectionwith a slightiy larger spacingof 3.35A. Worthy of special attention is that the 10 A reflectionacquired a tail toward its.low angle side.A very broad reflectionat about 11.5 A could be recognizedon its tailed reflection. Such behaviour is closely similar to that of the tailed re- flection accompanying the 10 A reflection in the crude specimen of the Kamikita material. After heating to 700oC., the weak and broad 2.45A 1000 5000 10000c Frc. 1. D.'l'.A. curves of the 26 A clay mineral from the Yonago mine Above: specimen in natural state. Below: specimen treated with piperidine. reflectionappeared; the intensitiesof the 10 A and 5 A reflectionbecame somewhalmore intense, but the 3.34A and 4.51A reflectionsbccame re- markably intense.The tailed reflectionwas still confirmed.After heating to 900oC., the intensitiesof the 10 A, 5 A, 4.5A and 3.35A are similar to thosein the specimenheated at 700oC., but the 26 A reflectionas well as the tailed reflectioncompletely disappeared, and the very weak 19 A re- flection appeared.In the specim-enheated at 1000oC., the reflections were weakened,except the 4.50 A and 3.40 A reflections.The result ob- l-ainedabove suggests that the 26A spacingseems to be related to hydrous statesof the 10A structure. Differential thermal analysis curve: The difierential thermal analysis curve of the specimenanalysed by r-rays showsthe broad endothermic peaks at about 600oC., and also between700' C. and 800oC., excepta clearendothermic peak between100' C. and 200oC. (Fig. 1, above).The specimenwas soakedin piperidinefor about 10 minutes, and dried on a water-bath. The specimenthus pretreatedwas analysedthermally (Fig' TO74 S. SI]IMODAAND T. SUDO 1). Its thermal curve sho'r,san additional exothermic peak between 600' C. and 700oC. as in the caseof montmorillonite or vermiculite. Chemicalcomposition: The specimenanalysed thermally and by n-rays was also analysed chemically. rts chemical composition is as follows; SiO, 43.177a;AlzOs, fi.5a/6; TiO2,O.5I7o; Fe2O3,0.267o; FeO,0.13/6; CaO,0.52/6; MgO, 0.657o;K2O,2.8470; NazO, 0.38/6; prOs,tr.; HrO (+) 10.4870;HrO (-) 7.757a,Total, 100.2370.Itis worthy of notice that the mineral almost agrees with allevardite (caillBre, Mathieu- Sicaud,and H6nin 1950;Brindley, 1956),except that the amount of po- tassiumis slightly larger and the amount of sodiumis smallerin the pres- ent material than in the caseof allevardite.The structural formula was constructed on the basis of the number of ions in the octahedral and tetrahedral positionsa"s 12 lor the sakeof comparisonwith that of alre- vardite.