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Kellyite, 4 Ne* Mn-Al Member of the Serpentine Group from Bald Knob

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Kellyite, 4 Ne* Mn-Al Member of the Serpentine Group from Bald Knob Ameilcan Mineralogist, Volume 59, pages 1153-1156, 1974 Kellyite,4 Ne* Mn-AlMember of the SerpentineGroup from Bald Knob, North Garolina,and New Dita on Grove3ite' DoNtrp R. Pnncon,Enrc J. EssnNE, Departmentol Geologyand Mineralogy,Thz Uniuersityol Michigan Ann Arbor, Michigan 48104 Wrr,treu B. SrvrlroNs,Jn., I Departmentof Earth Sciences,Louisiana State (Jnirsersity in New Orleans, New Orleans.Louisiana 70122 eNoWrrnun C. Blcrrow Departmentol Materialsand MetallurgicalEngineering, The Uniuersityof Michigan, Ann Arbor, Michigan 48104 Abstract Kellyite, (MngeMgosFe"*ozAl,.z)(Si,oALo)O.(OH)s,occurs as transparent, yellow, I mm_ sized grains dispersedwithin manganesecarbonates (principally kutnahorite) at the Bald Knob manganesemine, near Sparta, North Carolina. Associated minerals include galaxite, jacobsite, Mn-chlorite, alleghanyite, and sonolite. X-ray diffraction shows that it is isostructural with members of the serpentine group and thus the manganeseequivalent of amesite. Two polytypes have been recognized, a six-layer rhombohedral phase and a twd-layer hexagonal phase. The latter has spacegroup P6, and lattice parametersa = 5.438 1- 0.008A and c = 14.04!.0.01 A. The name is in honor of William C. Kelly, faculty member of the Department of Geology and Mineralogy, The University of Michigan. A mineral which yields a powder pattern identical to that of grovesite occurs with the kellyite. It is shown to be a one-layer chlorite having space group Cl or Cl, with lattice pa- - - - - rametersa 5.44A, b 9.40A, c 14.27A, a =.y:90.0., and B gB.lZ,.It is proposed that grovesite, formerly classed as a rnember of the serpentine group, is actually a manganese chlorite which is chemically similar to pennantite. Introduction serpentinegroup. Subsequent,detailed studies have The mineralogyof the manganesedeposit at Bald confirmedthis and shownit to be the Mn-equivalent Knob, near Sparta, North Carolina, was originally of amesite.The name, kellyite, is in honor of Dr. describedby Ross and Kerr (1932), who reported William C. Kelly, a member of the faculty of the two new minerals, alleghanyite and galaxite. We Department of Geology and Mineralogy at The recently collected from the waste dump at this lo- University of Michigan and an active contributor cality in order to obtain specimensof the alle- to the scienceof mineral deposits.The mineral and ghanyiteand galaxite.In severalof these samples the name have been approvedby the I.M.A. Com- we observedsmall grains (up to 1 mm in diameter) missionon New Mineralsand Mineral Names.Type of a transparent,yellow micaceousmineral. powder material is presentin the collectionsof the U. S. X-ray diffraction data indicated that it was a mem- NationalMuseum (SmithsonianInstitution) and the ber of the serpentinegroup. Sincethe rocks in which Department of Geology and Mineralogy, The Uni- it occurs are manganese-rich,we suspectedthat it versityof Michigan. might be a new manganese-rich member of the Associated Minerals lContribution No. 3t9 from the Mineralogicall-abora- Ross and Kerr (1932) described a large number tory, Department of Geology and Mineralogy, The Uni- of Mn-rich phases from the Bald Knob deposit in versitvof Michigan. addition to their descriptions of alleghanyite and I 153 1154 PEACOR, ESSENE, SIMMONS, AND BIGELOW galaxite. We have initiated a more extensive study regular-to-platyyellow tabletsand laths. It is wide- of the general mineralogy using electron microprobe, spread at Bald Knob; virtually every thin-section optical, and X-ray diffraction techniques,which will containingcarbonates shows at least a few grainsof be reported in detail elsewhere.Our results already light yellow kellyite. Other phases identified as indicate that there are two separateparageneses con- accessoriesin carbonate-richrocks are Ni-rich cat- sisting of carbonate- and silica-rich rocks, respec- tierite, cobaltite, arsenopyrite,chalcopyrite, pyro- tively. The carbonate-rich rocks consist largely phanite, zircon, rutile, apatite,alabandite, caryopi- of coarse-grained Ca-Mn carbonates with lesser lite, andMn-chlorite. amounts of alleghanyite, tephroite, sonolite, and The silica-rich samplesconsist primarily of quartz spinel-family minerals. The rocks have a distinctly and spessartine-richgarnet. Rhodonite and the Mn- banded appearancederiving from concentrations of amphibole tirodite are also both common phases. one or another of thesephases. X-ray diffraction and Thesesamples contain no kellyite.Another manga- electron microprobe analyses indicate that (com- nesesheet silicate, identified by powder and single- monly) the carbonate is near ideal kutnahorite in crystal X-ray diffraction as a member of the stil- composition, but a series of both Ca- and Mn-rich pnomelanegroup, is also presentin theserocks. It samples have been identified which appear to ex- generallyoccurs as dark brown foliated aggregates, hibit complete solid solution toward both the pure usuallyin contactwith quartz.In contrast,kellyite, Ca and Mn end member. The spinels are of two like serpentine,appears to be unstablewith excess types: a Mn-Fes* rich phase (jacobsite) and a Mn- quartz. Al rich phase (galaxite). These commonly occur together in intergrowths or as separate grains in the X-Ray Crystallography same specimens. The kellyite occurs exclusively in Weissenbergand precession photographs of kellyite the carbonate-rich samples usually interstitial to the yield resultssimilar to those reportedfor cronsted- carbonate grains or replacing galaxite. It forms ir- tite (Frondel, 1962; Steadmanand Nuttall, 1963, 1964). A hexagonalsubcell (a : 3.16,c : 14.10 A) is definedby a set of intenseand relativelysharp Tesre 1. PowderDiffraction Data for Kellyite, Caryopilite,and Grovesite reflections.The superstructurereflections are rela- tively weak and difiuse. The diffuse streaksparallel Keflyite* to c* indicatea high densityof layer stackingfaults. -calc -obs. hkl Two crystalswith superstructurereflections sharp aaz 7. 0 7.O 7.2 90 r\.3 !o enoughto definethe supercellhave beenexamined. oo4 3.51 L00 3 6lr B0 12.6 5 fr1 2 67 2.6T !o 2,78 70 ?. r l-00 has superstructurereflections which II2 2,5\ 2,53 5o 2.\9 roo \,'15 30 One of these a rhombo- 113 2.35 40 3 ,5',1 80 are barely discernible,but which define 006 2.3t1 2. oB jo 2.85 2a hedral lattice with a = 5.44 A and c = 42.13 A. ff! 2.r5 2.L5 10 f.95Il 3o 2.10 L0 1I5 l.95ir 1.95j{ r,724 ra 2.60 fo This is analogousto the 6Jayerpolytype of cronsted- 116 l. 10 r,617 20 Bo tite describedby Steadmanand Nuttall (1963). The 77lr r.768 2.t13 oo8 r,75i 2.30 20 secondcrystal yields superstructurereflections which rr? r.6rl+ r.612 10 2.10 5 300 1.570 f,570 2,O3 40 are significantlysharper than thoseof the first. It is 1,908 f5 5 a 2-layerhexagonal polytype with a = 5.44 A and c 118 r. \75 r. 477 10 r. 683 30 304 I 433 , r.585 20 = 14.04 A. Extinctions are consistentwith space 00,10 1.404 1, I+03 10 r. t?[ 30 group P63, and this crystal is also analogousto a 3oB l.r7o 5 l. 537 20 00,f2 1.1?0 f.440 5 cronstedtitepolytype describedby Steadmanand oo,rL 1.003 1.1128 5 Nuttall (1964). Although we have so far distin- 1.335 10 guished the occurrence of only two polytypes of f.300 5 kellyite, it may be predictedby analogywith cron- I.216 5 stedtitethat well-orderedcrystals having a variety 1.150 10 of stackingsequences may exist. The name kellyite f.059 15 shouldbe retainedfor all suchpolytypes. * EeKa, Mn-fi1tercd radiation; 714.5 ffi aiareter bbge-scherreE carera. *, CvKa, Ni-filtered radiation; 114-6 m diareter Debge-scherret careta. Powder diffraction data, including both Debye- Speciren tron Langban, tueden; univercitg ot Chicago Coflectioh- ... EeKa, Piltered radiationi 174.6 m diareter Debge-sctutret carera, Scherrerand diffractometerdata, are listed in Table data taken fton photograph ot tgp naterial Provided bg Dt' Rjchard Davjs, Edxish Museun ot NatDraf Eistarg. 1 for kellyite,along with comparabledata for caryo- KELLYITE, A NEW SERPENTINE MINERAL AND NEW DATA ON GROVESITE I 155 pilite and grovesite.Caryopilite, the Mn-equivalent flections are diagnostic of chlorite-group minerals, of serpentine,has a powderpattern similar to that of however. kellyite. The occurrence of essential Al in the At this stageof our investigation,the statusof octahedral layers of kellyite results in a significant grovesitewas uncertain.However, we subsequently contraction in the value of c as comparedto that of detecteda smallnumber of brown crystalsembedded caryopilite,and thesephases can thereforebe readily in kutnahoriteand closely associatedwith kellyite distinguishedon the basisof the magnitudesof the from Bald Knob, which yielded a Debye-Scherrer interplanarspacings corresponding to (00/) reflec- patternidentical to that of grovesite.The similarity tions.The latticeparameters for kellyite (a = 5.438 of the two patterns is rather striking, in view of the -+ 0.008A and c = 14.04-+- 0.01 A) wereobtained chemicalcomplexity of thesetwo phases.Single-crys- by least-squaresrefinement of the Debye-Scherrer tal diffraction studiesof one brown crystal confirmed data. it to be a chlorite (C1 or Cl; a = 5.444, b = 9.40A, c = 14.27A, o = y = 90.0o,I = 97oI2'). Comparison with Grovesite These lattice parametersagree well with those ob- Grovesite,(Mn,Mg,Al)3(Si,Al)2(O,OH)n was de- tained by Smith, Bannister, and Hey (1946) for scribedby Bannister,Hey, and Smith (1955) as a the manganesechlorite pennantite (except that the new mineral from the Benallt mine, Rhiw, Carnar- value of c is one half that of pennantite).Since the vonshire,North Wales. They concludedthat this chemical analysesfor pennantite and grovesite are phaseis "a member of the cronstedtite-berthierine- nearly identical, it seems clear that grovesiteis amesitegroup, with a structure based on the two- closelyrelated to pennantite.One unresolvedques- layer sheetsof the kaolin family . ," and that it is tion, however,involves the differencein powder pat- relatedto the Mn-chlorite,pennantite, as cronsted- terns betweengrovesite and pennantite,as noted by tite is to the Fe-chloritechamosite.
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