Canadian Mineralogist Yol.24, pp. 5l-54 (1986) RAPIDCREEKITE,A NEW HYDRATEDCALCIUM SULFATE-CARBONATE FROM THE RAPID CREEKAREA, YUKON TERRITORY ANDREWC. ROBERTS,H. GARY ANSELL ANDIAN R. JONASSON GeologicalSurvey of Canada,601 Booth Street,Ottowa, Ontario KIA 0E8 JOEL D. GRICE Mineral SciencesDivision, NationalMuseum of Natural Sciences,1026 Merivale Road, Ottawa,Ontario KiA 0M8 ROBERT A. RAMIK Departmentof Mineralogltand Geologlt,Royal OntarioMuseum, 100Queen's Park, Toronto, OntarioMSS 2C6 ABSTRAcT creekiteprdsente un bon clivage{100} et un clivagepar- fait {010}.Sa densit€ est de2.2l(l) (mesur6e)et2.239 (cal- Rapidcreekite,ideally Ca2(SO/(COr1.4gr6, is a new cul6e);elle n'est pas fluorescente sous l'ultraviolet. Elle est secondarymineral speciesfrom the Rapid Creek area, biaxialepositive, a 1.516(1),B 1.518(l),7 1.531(l),2V" northe.rnYukon Territory. It occurson bedding planesand (mesur6)45(3)", 2Vr(calcul6) 43 " ; l'orientationde I'indi- joint surfaces of a quartz-rich iron formation, as crystal- catriceest: X = c, Y = a, Z = b. Leshuit raiesles plus inten- line coatingsand spraysof white to colorlessacicular crys- sesdg diagrammede poudreobtenu par diffraction X [d tals. The symmetry is orthorhombic, space gogp Pcnb, en A(t)(afDl sont les suivantes:7.78(100)(200), with a 15.49(l), , 19.18(l), c 6.157(4)A, a:b:c 4.3| Q0)Q2r), 3. 88(70X3 r 1,400,23 I ), 3.I I (80)(421,40q, 0.808:1:0.321,Z = 8. Individual crystalshave a maximum 2.9t7 (50)(43 t), 2.797 (60',)(r 6r), 2.s5 5 (s0)(r 42,322) eI len&h of 2 mm and are elongate[001], with forms {010} 1.899(50)(303,580,233,082).Les analyses i la microsonde broad and {100}, {001} minor. The streakis white; lustre 6lectroniqueet I'analysethermogravim€trique * analyse des vitreous; brittle, fracture splintery; Mohs hardness 2; gaz6mis CIGA-EGA) donnent: CaO 36.3, SO3 26.1' CO2 cleavage{010} perfectand { 100} good; D(meas.)2.21(l), 14.0et H2O23.6, total 100.090(en poids). Le nom rap- D(calc.) 2.239g/cms; nonfluorescentin ultraviolet light. pelleI'endroit oir la nouvelleespdce a 6t6trouv6e. Rapidcreekiteis biaxialpositive, cr 1.516(l),0 1.518(l),r 1.531(l),2Z* (meas.)45Qr',2Zxk*.lc.) 4", indicatrix Mots-clds:nouvelle espbce min6rale, rapidcreekite, sulfate orientation X = c, Y=a, Z=b. The strongeliteight lines et carbonatede calciumtetrahydrate, Yukon, Rapid in the X-ray powder-diffraction pattern [d in A(I) (hkl)] are Creek,donndes de rayonsX, compositionchimique. 7.78(100x200), 4.3r(70)Q2r), 3.88(70X3l 1,400,23 l), 3.l I (80X421,002), 2.9r7(s0)(43 r), 2.797 (60)(l 61), 2.555(s0)(142,322)and 1.899(50)(303,580,233,082). INtnooucrtoN Microprobeanalyses and TGA-EGA gaveCaO 36.3, SO3 26.1,CO214.0and }J2O23.6, sum [email protected] wt.Vo.The name The Rapid Creek - Big Fish River area of the refers to the general locality. northern Yukon Territory is best knpwn for the unique assemblagesof phosphateminerals that occur Keywords: new mineral species,rapidcreekite, calcium sul- in a sequenceof Lower Cretaceous(Albian) iron- fate carbonatetetrahydrate, Yukon, Rapid Creek, X- stones and shales. However, recent surface- ray data, chemicalcomposition. weatheringhas resultedin the formation of many secondarysulfate and carbonateminerals, most of SOMMAIRE which havenot beenreported to date. Among these are aragonite,nesquehonite, dypingite, hydromagne- La rapidcreekite, dont la formule iddale est Ca2(SOa) site, gypsum, hexahydrite, halotrichite, epsomite, (CO3).4H2O,est une nouvelleespbce min6rale secondaire jarosite, natrojarosite and diadochite (a sulfate- d6couvertedans la r€gion du ruisseauRapid, dans le Nord phosphate). du Yukon. On la trouve sur les plans de stratification et Rapidcreekite,ideally Car(SOn)(CO).4HrO,is a de s€parationd'une formation de fer riche en quartz, sous new mineral speciesfirst encounteredin 1983,and forme d'enduits ou de gerbesde cristaux aciculairesblancs to date found only at one locality along the valley ou incolores. La symdtrieest orthorhombique, grolrpe spa- of (unofficially, CrosscutCreek) Rapid tiaTPcnb, a 15.49(1),, 19.18(1),c 6.157(4)A, a:b:c a tributary of 0.808:l:0,321,Z: 8. Lesmonocristaux ont, tout au plus, creek, at latitude 68"33'45',N, longitude 2 mm de longueur et sont allongds[001], la forme {010} 136"47'30'W. Rapidcreekiteoccurs as a secondary estlarge et lesformes {l@} et {001} sont eftoites.Ces cris- phaseon dilated joint-surfacesand beddingplanes taux sont fragiles, d trait blanc, 6clat vitreux et cassure in a blocky, quafiz-rich bed in the sideritic iron- esquilleuse;de duretd 2 sur l'4chellede Mohs. La rapid- formation. Minor amounts of glpsum and aragonite 51 52 THE CANADIAN MINERALOGIST are associatedwith rapidcreekite,and kulanite is slowly in heavyliquids, a measureddensity of 2.21(l) found on the holotype specimen. g,/cm3was obtained, in reasonableagreement with The mineral is namedfor the generallocality; both the calculated density of 2.239 g/cm3 for nameand mineral havebeen approved by the Com- CalSo)(Co)4}J2o. rnission on New Minerals and Mineral Names, Optical measurementswere made on a spindle I.M.A. The holotype specimen,consisting of a few stageusing sodium light O 589 nm). Rapidcreekite grams of material on matrix, is housedin the Sys- is biaxial positive, cu 1.516(l), 0 1.518(l) and y tematic ReferenceSeries of the National Mineral Col- 1.531(1).The measured2V*is 45(3)",close to the lection, at the GeologicalSurvey of Canada,Ottawa, calculatedvalue of 43" . Optical orientation is X: c, under cataloguenumber U346. Addiiional speci- Y:a andZ:b. mens of rapidcreekite are preservedat the Geologi- cal Survey and at the Mineral SciencesDivision, CRYSTALLOGRAFHY National Museum of Natural Sciences,Ottawa. Precessionsingle-crystal studies employing Mo Pnvsrcal ANDOPTICAL PRoPERTIES radiation of two crystal fibres showthat rapidcreekite is orthorhombic, spacegrovp Pcnb, with measurgd Rapidcreekiteoccurs most commonly as radiat- unit-cellparameters a I 5.45, b 19.16and c 6. I 65 A. ing spraysof white to colorlessacicular crystals, in The levels collected are hle0-hk2, 0kl-Skl and both isolatedclusters and pervasivecoatings on rusty- h\l-h\l. The X-ray powder-diffraction data (Table weathering quartz-rich iron formation. Individual l) were^refinedon l8 reflectionsbetween 3.005 and crystalsare colorless,transparent and acicular, elon- 1.655A for which unambiguousindexing was pos- gate parallel to [001], with forms {010}broad and sible, basedon precessionsingle-crystal films. The tl00l, [001]minor (Fig. 1), and approach2 mm in refined unit-cell par4meters arei q 15.49(l), b maximum length. The coarsermaterial has a length- 19.18(l), c 6.151(4)A, V tgZg.Z 43, and q:b:c to-width ratio of about 50:1. Bundlesof individual 0.808:I :0.321. The strongestdiffraction-lines are crystals appear lath-shaped. The mineral is brittle closeto thoseof gypsum,but the completepowder- with a white streak, vitreous lustre, splintery frac- pattern is significantly different from any mineral ture, and a Mohs hardnessof 2. Observedcleavages ofthe gypsumgroup. However, the powder data are are [010] perfect and {100} good. Rapidcreekiteis very similar to the unnamedcalcium arsenate @.D.F. nonfluorescentunder both long- and short-wave 29-294) described by Walenta (1972) from the ultraviolet radiation. Although the mineral dissolves Johann mine, Wittichen region, Germany. There seems little doubt that this latter mineral is the arsenateanalogue of rapidcreekite.This is further supported by the near-identity of their optical properties. TABLE I. X.RAY POVDER-DTFFRACTION DATA FOR RAPIDCRBEKITE r* a,i .*. a,i."t". hkl td oA .*. oi *t". hk'l 100 7.7t 7.75 200 2.3t2 2.t16 342 ln 2.211 371 20 5.tt9 ,.48 30 J 4.91 tt.9l l2l 2.245 t'l 2ll 2.2ta 2 l0 4.6t 4.67 5 70 s.3l 4.3t Z2l 2.212 l8l 3.tt 3lt 2.r7t 2,170 5t2 70 3.88 t.a7 r.00 t0 2.@l 2.6t 561 ,.85 231 20 2.q70 2.071 7ll 3.64 l4l 2.Ot7 072 40 ).66 3.66 321 10 2.*4 2,019 4t0 40 3.41 3,40 24r 2.035 r03 t.23 4ll 5 2.0@ 2.010 740 2b 3.72 3.20 060 40 1.986 l.9tt 5tt2 ).10 421 40 1.9' 1.949 Dr t0 ,.ll ,.a| 0m 1.907 303 251 1,E96 '80 20 1.005 3.0t2 50 t'6" 50 2.917 2.917 431 1.89i zrt 2.t80 122 1.a92 @2 1('b 2.871 2.a61 2C2 l0 L.E3t l.a, 243 60 2.797 2.79t l5l 5 1.786 1.7a7 491 2.754 351 1.766 722 1@ 2.743 2.730 l?2 l0 t.76t 1.75a 652 30 2.61 2.659 52r 1.757 6t0 2.555 142 t.7t0 l.7ll 503 2.555 50 2,549 122 l.68rr L6Ei 742 20 2.tt49 2.444 t32 t,655 1.656 4l!l 2.398 080 10b 2.)a6 2,t91 4t2 2.370 lto Ftc. l. Scanning-electronphotomicrograph of rapid- 114.6 mm Debyq.Scher.s Fsds @msa, Cu radatlon Ni tllt€ creekiteshowing typical habit of crystals.Lenglh of bar ocukGl.r4l 7tA), b=br€d llne is l0 rn.. irde:cd eith o 15.49.b l9.IE sd c 6.lr7i RAPIDCREEKITE, A CALCIUM SULFATE-CARBONATE FROM RAPID CREEK 53 too c .9 80 (tt .9 E ;60 c qt 1-'40 E o bzo o- 4000 2000 1500 1000 500 Wavenumbercm-r Ftc. 2. Infrared-absorptionspectrum for rapidcreekite.