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Home , Arseniosiderite, Childrenite, Collinsite, Hureaulite, Lithiophilite, Purpurite

American Mineralogist, Volume 59, pages 48-59, 1974

l. Jahnsite,Segelerite, and ,Three New TransitionMetal PhosphateSpecies ll. Redefinitionof Overite,an lsotypeof Segelerite

Pnur BnnN Moone Thc Departmcntof the GeophysicalSciences, The Uniuersityof Chicago, Chicago,Illinois 60637

ilt. lsotypyof Robertsite,Mitridatite, and

Peur BmaN Moonp

With Two Chemical Analvsesbv JUN Iro Deryrtrnent of GeologicalSciences, Haraard Uniuersity, Cambridge, Massrchusetts 02 I 38

Abstract

Three new species,-jahnsite, segelerite, and robertsite,-occur in moderate abundance as late stage products in corroded -heterosite-ferrisicklerite-rockbridgeite masses, associated with leucophosphite,, , laueite, etc.Type specimensare from the Tip Top , near Custer, South Dakota. Jahnsite, caMn2+Mgr(Hro)aFe3+z(oH)rlPC)oln,a 14.94(2),b 7.14(l), c 9.93(1)A, p 110.16(8)", P2/a, Z : 2, specific gavity 2.71, biaxial (-), 2V large, e 1.640,p 1.658,t l.6lo, occurs abundantly as striated short to long prismatic crystals, nut brown, yellow, yellow-orange to greenish-yellowin color.Formsarec{001},a{100},il2oll, jl2}ll,ft[iol],/tolll,nt110],andz{itt}. Segeierite,CaMg(HrO)rFes+(OH)[POdz, a 14.826{5),b 18.751(4),c7.30(1)A, Pcca, Z : 8, specific gaavity2.67, biaxial (-), 2Ylarge,a 1.618,p 1.6t5, z 1.650,occurs sparingly as striated yellow'green prismaticcrystals, with c[00], r{010}, nlll0l and qll2l } with perfect {010} 'It is the Feg+-analogueofoverite; a restudy on type overite revealsthe spacegroup Pcca and the ideal formula CaMg(HrO)dl(OH)[POr]r. Robertsite,carMna+r(oH)o(Hro){Ponlr, a 17.36,b lg.53,c 11.30A,p 96.0o,A2/a, Z: 8, specific gravity3.l,T,cleavage[l00] good,biaxial(-) a1.775,8 *t - 1.82,2V-8o,pleochroismextreme (Y, Z = deep reddish brown; 17 : pale reddish-pink), @curs as fibrous massesand small wedge- shapedcrystals showing c[001 f , a{1@}, qt031}. It is tabular paraltelto {100}. The color is shiny black, blood-red in thin splinters, chocolate brown. Mitridatite, carFes+n(oH)o(Hro)glPodr, a 17.52(2),b lg.1r4), c 11.25(2)4, p 95055" A2/a, Z :8, specificgraity 3.24,a1.785,F o t : 1.85,2V 5-10o,pleochroismextreme (Y' Z - deep greenish-browl, X : pale greenishyellow), shows a{100},^c{001} arrd ul423l. Arseniosiderite, carFes+(OH)o(Hp)glAsOrlr has a 17.76,b 19.53,c 11.30A, p 96.00based on the powder data. These speciesare isotypes of the robertsite structure.

Introduction oped crystals. It is approPriate,for this reason, to commencewith a detailed description of the para- Rarely doesan investigatorin descriptivemineral- genesisof these since their compositions ogy have an opportunity to announcethree species leave little doubt that their formation was due to the new to scientific intelligence which not only occur presenceof Caz', Fe3*,Mn2', Mnt*, Mg'*, [POn]t-, intimately associatedbut also appear as well-devel- and (OH)- ions in solution at low temperature.

48 THREE NEW TRANSITION METAL

Following this paragenetic discussion, the crystal a. The aquated oxidaion products of triphylite- chemistry of each speciesshall be discussedsepa- rately. The secondaryphosphate paragenesis of the Tip The type specimensoriginate from the Tip Top Top pegmatiteappears to fall into two closelyrelated pegmatite,near the village of Custer, in Custer but distinct categories:the products of direct solu- County, South Dakota, although other localities tion, oxidation, and recrystallizationof the parent have alsocome to light and one species(robertsite) triphylite-lithiophilite and the products involving the has a Fes*-analogue(mitridatite) so widespreadin addition of Ca2*and Mg2*cations. We haveexamined its occurrenceto suggestthat the phaseshould elicit by electron microprobe analysis remnant primary considerableinterest in its crystal chemistry.The triphylite occurring in the interior of the zone of oxi- Tip Top pegmatite(NE 7a, SW 7+, sec. 8, T.4S, dation and aquation and have obtainedthe composi- R.4E) is one of severalin the regionof the central tion Li(Fee7sMns.22Mg.o.ro)[POn].Since the late Black Hills where a great abundanceof triphylite- stageCa-Mg rich phosphatesoccur locally but occa- lithiophilite appeared as an accesorycore sionally in sufficientabundance, it is difficult to imag- arrd was exposedduring the course of activ- ine a contribution of the Ca2*and Mg2- cationsfrom ity. These crude giant crystals of triphylite suffered the parent phosphates;it is proposedthat thesecat- extensiveretrograde oxidative and metasomaticre- ions were introduced at alate stagefrom a separate actions which resulted in the ferrisicklerite-sicklerite source and were added to the pool of cations pro- seriesLi1-,Fe3*,(Fe2*,Mn'-)r.-r[POa]; the heterosite- vided by the the parent phosphates. series (Fe3*,Mn3*)tPOn];and the rock- The oxidation and aquation of triphylite leads bridgeite-frondelite series (Fe,Mn),-Fe'.r(OH)s directly to the formation of rockbridgeite or ferri- [POrle.Vuggy cavitiesin thesephases contain a host sicklerite, where ferrisicklerite may in turn be oxi- of late stage hydrated transition metal phosphates. dized further to heterositeor aquatedto,form rock- Since casual inspection of such associationscan be bridgeite. These phasesare observed as among the unreliablein identificationof species,great care was most persistent products of oxidation-aquation of taken in this study to examineall distinct phasesby triphylites in granitic throughout the X-ray single crystal and powder diffraction tech- world. Since the isoelectronicpoint of Fe3* cation niquesand, whenevernecessary, to establishidentity occurs at lower pH valuesand earlier than Mn2* and by comparison with descriptionsof type materials. the Fe2' remaining, leucophosphite crystallizes at Phasesdiscovered in thesecavities include leucophos- low temperatureswhere water ligands are stable. phite, KFe3.2(OH)(HzO)[POa]z.HzO, as lovely The solution becomesprogressively enriched in Mnz*, greenish-grey,purplish-pink to deep amethystine which crystallizes later in hureaulite. At the final prismatic crystals; hureaulite, (Mn,Fe),-s(HzO)n stages,laueite and mitridatite appear.Here, oxidation [PO3(OH)]2[PO+]2,as pale yellow, to pale pink to may produce Mn3*, so that bermanite forms. With red-brown prismatic crystals; collinsite, Ca2(Mg, the depletionof , ca Mn.s (O, Fe") (H2O)s[POe]2,as colorlessto white radiating [POa]'-, OH)16.2H2O, crystallizes.Thus, the sequencetri- sprays,lath-like crystals,and flattened chisel- phylite-ferrisicklerite- rockbridgeite- leucophosphite, shaped rosettes;hydroxylapatite, Cad(OH)[PO+]s, hureaulite * laueite-mitridatite-bermanite-todorokite as rounded colorlesshexagonal prisms; , appearsrepeatedly at the Tip Top, White Elephant ca Ca6Mg[PO+]e,as colorlesssimple rhombohedra; and Linwood pegmatitesin the Black Hills; at Ha- bermanite,Mn2'Mns-2(OH)r(HrO)n[POn]e, as deep gendorfStid, Bavaria; at PalermoNo. 1, New Hamp- reddish-browndruses of thin tabular crystals;laueite, shire; and at the Sapucaiapegmatite, Brazil. Mn2-Fe3.2(OH)z(HzO)o[POl]z.2HzO,as striated orange laths; mitridatite, Ca3Fes-a(OH)u(HrO), b. The addilion ol Cazrand Mg* [POn]n,as thin brittle greenish-brownplates and dull olive-greenstains; and the new speciesjahnsite, Collinsite, hydroxylapatite, whitlockite, and the CaMn'.Mp ( HzO) eFe3.z( OH ) 2[PO4]4; segelerite, Ca three new speciesare not rare at the Tip Top peg- Mg(H2O)aFe3.(OH)[POe]zi and robertsite, Cas matite. In addition, they have been observedfrom Mn3"a(OH)6(HrO)s[PO4]r.For a generalreview of the White Elephant pegmatite,having formed under the myriad pegmatite phosphates,the reader is re- similar conditions. Mitridatite is a particularly per- ferredto Moore (1973). sistent phase at all stagesof late crystallizationand 50 PAUL B, MOORE occurswidely as stainscoating the silicatessuffound- quently occur as parallel aggregates,twinned by ing triphylite crystals at practically every pegmatite reflectionon c[001]. Large crystalsmay be up to where triphylite occurs, suggestingthat mitridatite 5 mm in length, though 0.1 to 0.5 mm are most is an important low temperature phase. Paragenti- typical.The forms includec{001f , c{100f, t{2011, cally, the Ca2*-and Mg'Lbearing minerals occur at jlz}rl, k{iol}, /{0lrl, m{llof and nIill] with the sequencewhere leucophosphiteand hureaulite striaeon jlz0ll and all00l. A typical development crystallized. Robertsite appears in several genera- is presentedin Figure l. tions: as shiny black botryoidal aggregatescoating Analysis of the reticular density (based on the the cavity walls upon which are implanted jahnsite X-ray cell) reveals that the form frequenciesap- and collinsite, and as reddish platy rosettes im- proximately follow the order of descendinginter- planted upon theseminerals. In severalspecimens, it planar spacings(Table la). The form blOlOf is occurs as the sole mineral with stubby shiny black consistently absent; examination of single crystal wedge-shapedcrystals lining the cavitiesin the same. data revealsthat this plane is of zero intensity.Table Collinsite, hydroxylapatite, and whitlockite usually la suggeststhat some crystals of jahnsite should appear as the last minerals to crystallize,encrusting reveal l2llf and {lll}, but none of the crystals the rather abundant jahnsite. The author suggests submitted to morphological examination presented that the Fe3* remaining in solution crystallized as thesefacets. jahnsite pure Ca-Mg phosphates with the essentially X-ray data crystallizinglast. A partly indexed powder pattern is oftered in JAHNSITE Table 2a. Caution was taken to roll the ground sam- *r1oH;, ple into a small spherewith rubber cement.Through- CaMn2* Mgr(Hro), Fe' 1POn1, out this study, the powder data were indexedon the D es cr i p tiu e basis of the stro,ngsingle crystal intensities.Compu- The new speciesjahnsite occurs as tabular short tations of the interplanar spacingswere made from to long prismatic crystals with vitreous to subada- the single crystal studies. mantine luster of a nut-brown, purplish-brown, yel- Table 3a provides the structure cell data. In ad- low, yellow-orange,or greenish-yellowcolor. It can dition, we have solved its crystal struotureand have be easily confounded with laueite, pseudolaueite, refined the results to R(hkl) = 0.09. This allows stewartite, and . Experience has shown that almostcertain distinctionfrom theseother phos- phates can be achievedby analysisof crystal mor- phology. Persistentstriations parallel to the prism (=[010]) distinguishit from hureauliteand leuco phosphite.Laueite and stewartiteusually revealtheir triclinic character.Metastrengite usually possessesa delicate pink color not observedin jahnsite. Chil- drenite in well-developedcrystals almost invariably shows good orthorhombic development with per- sistentp{lII} ands{121}. The specific gravity of jahnsite is 2.706 (pyc- nometer), 2.718 (sink-float in methyleneiodide- toluene), computeddensity 2.715 gm cm-3, hard- ness4, cleavage{001} good.The mineralis soluble in dilute HCI solution.

Crystal morphology Crystals are commonly well-developedand eu- AB hedral, (2/m), monoclinic holosymmetric striated FIG. l. Crystal of jahnsite showing the forms c {001}, a { 100}' parallel to [010], short to long prismatic parallel i!2}rl, jlzol l, &{i01l,l{0r1}, n{110f, and z{ill}. Tip Top to [010],often tabular parallelto a{100f. They fre- pegmatite. A. Plan. B. Clinographic projection. THREE NEW TRANSITION METAL PHOSPHATES 5l

Tnnr.B l. Jahnsite and Segelerite. Descending Interplanar Mg-O octahedra in the structure, we propose the Spacings, Intensities, and Appearance of Forms ideal formula CaMn2.Mg2( IIpO ) gFe8.e( OH ) ?[PO4]4, JAHNSITE SEGELERITE of which there are two formula units in the cell. * hkl d(hkl) l/Io Appearance* hkl d (hkl) I/Io Appearance properties 001 9.32 10 x 010 18.75 > Z > X, with X pale pulple, 030 6.25

2lt q.gq < 6 and Berman (1934), the ideal fonnula, and the aver-

rlr q.gr < 6 age observedspecific gravity, (n) calc = 1.668.

20r q.86 < I 202 4.70 < 1 Tlrr"e 2. Jahnsite and Segelerite. Powder Data

*G=prese4t,a=ab6ent) a. JAHNSITE b. SEGELERITE d(obs) d(calc) !/I_g !\l !/!S d(obs) d(calc) !!l for a precisedescription of the jahnsitecrystal chem- 9.27 9.320 001 9 9.3I 9.376 020 istry and the establishmentof a correct formula, .I 7.08 7.OI2 200 I 5.7rt 5.815 220 2 6.12 6.360 II0 6 5.34 5.372 t2l which otherwisewould be a difficult and uncer,tain 4 5.6b s.683 l-It q q.97 5.01-q zLL problem. Chains of Fe3.-OH-Feg* corner-sharing s,667 0lI q 9.65 q.688 0't0 q.9I r{2 octahedra run parallel to 6 brd 9.9 2LI 2 3.936 3.962 2{r0 the b-axis and link to r+.908 III 5 3.7 29 3.706 400 [PO+]* tetrahedra; alternating Ca-O and Mnz'-O q q.63 q.660 002 5 3. q2I 3. 'rq6 q20 distorted octahedraledge-sharing chains also run in 3 q.05 rt.075 II2 2 3.253 3.255 4tl. 3 3.90 3.91-0 3I0 3.224 2L2 the hdirection, forming denseslabs parallel to {001}. I 3.723 3.733 qol I 3.163 3.18S q30 These slabs are bridged by the [POn]* tetrahedra 5 3.s22 3.5qo 3rz 3 3.059 3.083 3r+l q00 qqo which link 3.506 r0 2.868 2.907 by corners to the aquated Mg-O octa- 3 3.q16 3.q26 q02 2.882 0q2 hedra. The structure reveals a novel ligand stereo- 3 3.268 3.28q 3II 2 2.813 2.82L I6t isomerismabout the octahedralcorner-chains which 2 3.I6s 3.165 22I 4 2.583 2.577 rrtz 5 2.950 2,962 r+01 3 brd 2.368 2.389 q60 was predicted on combinatorial grounds by Moore 8 brd 2,825 2.A6? 403 2.379 062 (1970). It is allied to the childrenite-eosphoriteand 2.833 022 3 2.107 2.296 2L3 tt 2.575 2.579 q2r I 2.253 2.275 qq2 laueite-pseudolaueitestructures. 2 2.t1I7 2.q24 402 3 2.f91 3 2.3rt1 2.3r+9 q04 ) ) tt1 Chemical analysis 2.340 6r.r r 2.060 2.122 612 I 2.026 Several electron probe analysesof jahnsite were 3 2.002 2.007 tt22 c 1,988 made by Mr. T. Solberg utilizing apatite, wollaste 2.007 q03 c 1.963 qzq nite, wyllieite, and MgO standards. 3 1.958 1.962 I r.925 Owing to the q .r.gqs t.95I 02q lteo? brittle characterof the crystals,the jahnsite samples I.9q7 405 3 1,8'+q were not polished and consequentlythe quantitative 4 1.870 1.866 802 3 1.819 2 I.787 1.78rr 0rr0 3 r.733 results in Table 4a arc consistentlylow. Thus, com- r L.777 2 r.697 putations of the cation composition were based on 2 I.746 r I.667 an integral number of 2 r.608 atoms. Valence r .1.669 r I.593 stateswere inferred by the analysis r 1.6q2 and the water content was determinedby the Pen- q 1.573 2 1.5r+0 'r I.5r+8 1 t qtq field tube techniqueconducted by Dr. A. L. Lingard 3 I.52q I l.tt49 of South Dakota School of Mines and Technology. 3 l.rr95 2lu?q SettingP = 8.0, the analysis + 20 line6, -Iess than 3 3 r.3r+6 computesto 2 I lqq

2 1.305 Ca2.eMn2*2.sMg.rFet*a.sAlo.s 3 1.296 (oH)4.1[PO4]8.o.15.8 H2O. 3 t.25q + 15 linesr Iess than 3.

Noting that all water molecules are bound to the (Fe,/Mn racliation, ll4.6m camera dimeteri filr corrected for shriikage) 52 PAUL B. MOORE

Tasln 3. Jahnsite, Segderite, and Overite. Structure C-ell Data

a. JAHNSITE b. SEGELERITE c' oVERITE rr+.78 e6) I4.e4 (2) t+.826(s) 18.78 ldl 7 .14 (1) 18.7 51(r+) sdl e. e3(r) 7 .3o_7(L) 7.lll F l-10.16(8) o Pcca PUa Pcca 2.53 specific gravity 2.706t 2.7!8 z-o I 2. q8 dssity (em crfl 2.7L5 2.610 (oD Po4] caMs(HzO) (OD t PO4l car-rg(Hro) (olDI Poq]2 fomla caMg.(Hao) ,!hz+re:+ 2[ rl +Fe3+ 2 uAr 2 8 I

Tip Top pegmtite. Refined coordinates frcm PAILRED diffractometer' h Tip Top pegmatite. Refined coordLnates fM flICXER diffractometer' c. Fairfield Utah. Axia1 data and itv of Iarsen

Occurrences variable amount at the White Elephant,Bull Moose, Big Chief, and Linwood pegmatitesin the Custer Jahnsite is a relatively abundant mineral in the region of South Dakota, invariably with hureaulite low temperature phosphateparagenesis at the Tip and leucophosphite.At the Linwood pegmatite,much Top pegmatite.It usually occurswith leucophosphite, of the bright yellow friable material filling cavities in hureaulite, and collinsite, but granular massesup to heteroeiteand associatedwith collinsite and robert- 5 cm acrossconsisting solely of the new mineral fill site provides a powder pattern identical with jahn- cavities in ferrisicklerite. These massesare aotually site. Nut-brown striated crystals occur as warty ag- denselyinterlocking turbid dull yellow-orangecrys- gregateswith laueite and strunzitefrom the Palermo tals invariably twinned on resulting in a {001} No. 1 pegmatite,North Groton, New Hampshire. pseudo-orthorhombicappearance. It also occurs in A related compound occurs in moderate abun- danceas orangesplinters intergrown with 1= replac- Tlst.n 4. Jahnsite, Segelerite,and Overite. Chemical Analyses ing?) coarse fibrous black rockbridgeite from the Hampshire. a. JAHNSITE b. SEGEIERITE c- oVERITE Fletcher pegmatite,North Groton, New 123456 It correspondsto the "golden rockbridgeite"of New England collectors. The unit cell and space group CaO 6.6 6.9 13.6 I4.0 16.1 15.I are similar to those of type jahnsite, but the optical 9.4 9.9 9.s 10.r 1r.2 10.9 Mgo and physical pro,pertiesindicate a different composi- WrO 8.0 8.7 0.0 tion. This may be related to'the "xanthoxenitelike Fe20 15.l 19.6 16.4 20.0 3 phase"incompletely described by Mrose ( 1955). Yet A1203 )1 0.q 13.7 13.7 anotherrelated phase occurs as tan, tabular, twinned P-0. 33.1 15.6 38.9 38.3 crystals coating rose from the Taquaral peg- Hzo 18.8 19.9 19.r 20.3 22.OC 22.O matite, Minas Geraes, BtaztT. It, too, provides a

92.2 100.0 92.I I00.0 10r.9 100.0 structure cell akin to jahnsite, and Anr electron aluminumanalogue IARL probe analysisshows that it is the electron probe analysis conputed as oxides. Unpolished crystals: T. Solberg, malyst. Water detemined by Penfield of jahnsite. Both compounds are presently under tube: A. Lingard, analyst. further investigation. 2For (oH) Po4l caMs2(Hzo) sr'.r.r2*F":+ 2[ 4. 3See loss upon fusion. it;. v,later detemined by weight Name qror caMg(Hro)ure3+1otq Iroulr. The Commissionon New Minerals and Mineral SARL ulectro. probe analysis computed as oxides. l'later from Names (IMA) has approved the name jahnsite crystal: A' J. Irving' analyst. Larsen (1940). Polished prior to publication. It is a pleasureto christen this 6For CaMg(Hro)uAtioHlIro,r) r. magnificentspecies iahnsite after ProfessorRichard THREE NEIY TRANSITION METAL PHOSPHATES 53

H. Jahns, outstanding scholar of pegmatites, and that of overite. Overite was described as a new Dean of Earth Sciences.Stanford Universitv. speciesby Larsen (1940) who proposedthe formula CagAle(PO+)r(OH)o'15HrO,Z = 2, and the cell SEGELERITE dataa 14.75,b 18.74,c 7.12 A, spacegroup Bmarn. Through the assistanceof Mr. John S. White, Jr., CaMg(HrO)rFe'*(OHXponl, we obtained some single crystalsfrom the type ma- D escriptiaemineralogy terial, bearingU.S.N.M. No. R7898. X-ray, Weis- senberg,and precessionphotographs about the c-axis This new species closely resemblesjahnsite, to conclusivelyshow that the spacegroup is Pcca,iden- which it is chemically related, but is easily distin- tical with that of segelerite.Recently, we examined guished by its relatively simple orthorhombic mor- the crystal chemistry of overite by electron probe phology, pale green color, and long prismatic de- analysis,following the proceduresused for jahnsite velopmentwith nearly squarecross-section. Segelerite and segelerite.The original formula is in error: appears to be much less frequent than jahnsite; it overite is the aluminum analogueof segelerite,with occurs as striated prisms along joint fractures in the formula CaMg(IIrO 4Al (OH) dense ferrisicklerite-rockbridgeite,usually in close ) [POdr. The overite analysiswas performed by Dr. A. J. association with collinsite, minor hydroxylapatite, Irving who used diopside,anorthite, and wyllieite as and globules of red-brown robertsite. The color is standards.Since the crystal of overite was polished, pale yellow-green, lively chartreuse, inclining to it provided excellent results as shown in Table 4c. colorless.The cleavageis {010} perfect,hardness 4-, specific gravity by sink-float in methylene iodide- Chemical arnlysis toluene2.67.The computeddensity is 2.610gm cm-s based on the structure cell and ideal formula. It is Anr electron probe analysesrun simultaneously solublein dilute HCI solution. with the jahnsite on several small single segelerite crystalsgave the resultsin Table 4b. The water con- Crystal morphology tent was determinedby weight loss upon combustion since there was no evidence for oxidizable ionic Crystalsare up to 0.5 mm in length; orthorhombic species. (2/m 2/m 2/rn), and striated parallel to the prism Based on P = 16.0, the cation ratios establish which is [001]. The cross-sectionshows a nearly Cas rAlo.r['POn]te. o( OH ) z I' 30.7 H2O square outline, with lustrous a{ 100}, D{010}, 3Mg6.6Fe3.z. suggestingthe ideal formula CaMg(HeO) aFes-( OH ) m{IlO} and.q{l2l}. A typical developmentis shown with eightformula units in the cell. in Figure 2. The analysisof reticular densityin Table [POn]2, 1b showsthat the developmentconforms to the space group and structure cell shape.

X-ray data A partly indexed powder pattern is offered in 'Iable 2b, and the single crystal study is summarized in Table 3b. We note that the structure cell is re- lated to that of jahnsite,but it is not possibleto trans- form the jahnsite structure into that of segelerite continuously without changes in order of ligand groupingsaround the Mg-(O,HzO) octahedra,and we concludethat a stereoisomericrelationship exists between the two species.Toward this end, we are investigatingthe structure of segelerite. AB Ooerite: an isotype showing the forms D a 100 We mention the closesimilarity betweenthe struc- Fro. 2. Crystal of segelerite {010}' { | , mlll}l, and qll2l |. Tip Top pegmatite. A. PIan' B. ture cell and crystal morphology of segeleritewith Clinographic projection. PAUL B. MOORE

Optical properties Robertsite is moderately abundant, at least lo- The type segeleriteis biaxial (-), * 1.618,p cally, and is probably rather widespread,especially 1.635,y 1.650 -r 0.003, 2V large.The absorptionis in pegmatiteswhere triphylite occurs in abundance. Z (yellow)> X,Y (colorless),with X: b,Y = a, It is easilyconfused with the rockbridgeite-frondelite group Z=c. of minerals, which commonly occur as shiny black to deepreddish-brown fibrous masses.The key Occurrence differencesinclude color and specific gravity. Rock- So far, the Tip Top pegmatiteis the only locality bridgeite sliversare bluish to greenishin tint; robert- for segelerite.It usually occurs in intimate associa- site is reddish-brownto deepblood-red. In methylene tion with collinsite and hydroxylapatite. According iodide, fragments of rockbridgeite-frondelite sink to the crystal structure analysisof jahnsite, the or- while those of robertsite (and mitridatite) float. dered Mn2* cations evidently stabilize that mineral. Robertsiteoccurs as fine feathery aggregatesof deep Sincejahnsite is evidently rather abundant,sufficient red to bronzy plates, botryoidal aggregatesof shiny Mn2*was apparentlyavailable in solution to promote black fibers, shiny black plates, and lustrous small its formation. As Mn2* is depleted,segelerite forms, wedge-shapedcrystals. A spectacularspecimen, mea- providing there still remain some Fe3' cations in suring 6 x 7 cm in area, showsthe mineral as broad solution. Segeleriteappears later than jahnsite and plates up to 5 mm across which are grouped as for this reasonis found in close associationwith the bunchedradial aggregatesalong a in a dense Ca-Mg phosphatesrather than leucophosphiteand rockbridgeite-ferrisickleritemass; its lustrous black hureaulite which have crvstallized earlier with the color is reminiscentof hematiteand manganitethough jahnsite. it lacks their steel-greytint. Robertsite lines cavities in rockbridgeite and ferrisicklerite upon which are Name placed crystals of leucophosphite,jahnsite, and hu- Mineral The Commissionon New Minerals and reaulite. A late generation of this platy robertsite pub- Names (IMA) has approvedthe name prior to often is deposited upon these minerals. Another of this lication. The lustrous well-developedcrystals specimenshows a dense mass of deep red-brown honor new segeleritemake it fitting to massive robertsite in which cavities are lined with Mr. Curt G. Segelerof Brooklyn, New York, ama- lustrous wedge-shapedcrystals of the same.It is this micro- teur mineralogist,whose superb collection of specimenfrom which crystalssuitable for X-ray and mounts, especiallyof pegmatiteplosphates, reveals rnorphological study were obtained. All specimens identifi- the care and meticulousnessof his mineral originated from the Tip Top pegmatite.The mineral cations through optical and microchemical tech- also occurs at the Linwood pegmatitein a paragene- niques. sis similar to the Tip Top material, and in small ROBERTSITE amounts at the White Elephant and Gap Lode peg- *o1oH)6(Hro)3 matites. ca, Mn' [ Po4]4 The color is shiny black, blood-red to reddish- D es cr ip ti te mineralogy brown in thin slivers, streak chocolatebrown, hard- Evidence provided here supports the statement ness3.5, cleavage{100} good. The specificgravity that robertsite,mitridatite, and arseniosideritebelong of the crystalsis 3.17 (sink-float in methyleneiodide- to the same structure type. This is of considerable toluene),3.13 (Bermanmicrobalance, on botryoidal interestsince mitridatite is a stableand persistentlow fibers). Finely fibrous material is silky, deep reddish- temperature phase and occurs frequently as dull- brown, resembling goethite. Thin plates are remi- green stains coating wall rocks in pegmatiteswhich niscent of lepidocrocite. carry transition metal phosphateminerals. Crystal morphology Work on the entire mitridatite problem has been hindered through lack of suitable single crystal ma- Single crystals of robertsite suitable for detailed terial. All three phases characteristicallyoccur as morphological and X-ray study are rather rare, and fine fibrous masses of thin curved plates, dense only one specimenprovided adequatematerial for nodules,and stains.We shall elaborateon the crystal the crystal structure analysisnow in progress.Mea- chemistry of the robertsite-mitridatite-arseniosideritesurablecrystals are thick tabular and wedge-shaped; group as a conclusionof this study. very thick crystals are pseudo-rhombohedralin ap- THREE NEW TRANSITION METAL PHOSPHATES 55

pearance.Crystals range from 0.05 to 0.5 mm in of the most remarkable of Nature's mineralogical maximum dimension. They are frequently twinned legacy. In addition, Mr. Roberts maintains a con- by rotation normal to {100} and often involve rota- tinued interest in the minerals of the Black Hills tions by multiples of. */3 radians owing to the pegmatites,particularly the rarer $pecies,and his pseudo-hexagonalcharacter of the crystal subcell. compendious knowledge of minerals in general has Untwinnedcrystals show prominent a{100}, c{001} consisently provided many fine specimens for re- and p{031}, and establishbeyond doubt the mono- search. clinic symmetry of the species.In addition several doubly terminated crystals established the mono- The Mihidatite and Arseniosiderite Problems: clinic 2/m holosymmetry.A typical developmentis Isotypy with Robertsite shownin Figure 3. a. Mitidntite X-ray crystallography Mitridatite is a name applied to many colloidal Determination of the correct space group and and fine-grainedsubstances which occur as nodules unit cell parametersproved difficult owing to the and gumlike massesat numerous localities in the rarity of suitable single crystals. Despite the rather Kertch and Taman peninsulasin the Soviet Union. lustrous and even appearaoce of many crystals, The most recent study on the problem, an investiga- goniometric examination revealedtwinning by rota- tion on mitridatites by Chukhrov, Moleva, and tion of + r/3 radianson {100}. X-ray photographs Ermllova (1958), provides powder and optical data. of the same were almost impossible to decipher A firm knowledge of the mitridatite chemistry was until a small untwinned fragment was secured. Rotation about [010], [001] and [00], and Weissen- berg photographsof the h : O, I : 0, k : 0 to 4 A c q levels, establishedthe monoclinic end-centeredcell in Table 5. It exhibits a profound and persistent substructurewhich obeysthe sameextinction criteria and requiresb (sub) : b/3. After the b-axisrotation photograph was prepared, successiverotation pho- tographswere obtainedby regluingthe crystal ! r/3 radians aw4y from b. The three photographs,whose axes are perpendiculat to a*, reveal a pronounced pseudo-hexagonalcell. However, only the b-direction afforded evidence of a mirror plane although the axial translationsare roughly of the samemagnitude for all threephotographs. This conclusivelyestablished the monoclinic character of the species.We note that {3 6(sub) : 11.27A nv B A partly indexed powder pattern". appearsin Table 5. Sincethe chemicalanalysis and optical properties shall be correlated with those of mitridatite and arseniosiderite-as are the X-ray data-we provide further discussion of the new speciesin the next section. Natne The name robertsite was approved by the Com- missionof New Minerals and Mineral Names,Inter- national Mineralogical Association. It is a privilege to name this interestingspecies after Mr. Willard L. Frc. 3. Crystal of robertsite showing the forms c[001 1, Roberts, Mineralogist,South Dakota Schoolof Mines a{100}, and 4{031}. Tip Top pegmatite.A. Plan. B. Clino- and Technology,in whose private cabinet are some graphic projection. PAUL B. MOORE

Taur,r5. Robertsite,Mitridatite, and Arseniosiderite.Structure Cell Data

s,G[) 17.36 (2) L7"s2(2) 17.76('{) !6) rs.s3(s) le .3s(4) 19"53 s6) 1r.30(3) II "2s (2) 11.30 B 96.0() 9s.e20(8) I e6.o]

space group A2/a A2/a lAz/a7

specific gravity 3.13,3.17 3.24 3"58,3.60

density (Em cm-31't 3.05 3.08 3.59 ?+ ?+ formula (oH) (Hzo) carFe[' (oH) (Hzo) Poq] carFe[' (o]D (Hzo) ca3Mni+ 6 3[ Po4]4 6 3[ 4 6 '[Asoulu I 8 I * The density is computed from ideal formula and the ceII data. *Robertsite.I Tip Top pegmatite. From rotation and Weissenberg data. 2Mit"id.tit". White Elephant pegmatite. From rotation, Weissenberg and precession data. -Arseniosj.derite"? Mapimi, Mexico. Fr-om partly indexed powder data, matched with (1) and (2). Drrors in b and c are probably i 0.1 A. hindered by the lack of coarse-grainedmaterial, isotypy with robertsite, including similar sub- and in particular of singlecrystals. In this study, we offer super-structurereflections. Like robertsite,the strong evidenceof specificstatus for mitridatite and conclude substructure reflections predominate, resulting in on the basis of powder diffraction patterns that the similar and relatively simple X-ray powder patterns. material of Chukhrov et al is the fine-grainedequiva- Combinationsof a{100} and ol423l result in a lent of our specimensand that the materials are in polyhedron (Fig. a) with profound pseudo-rhom- fact the samespecies. bohedral appearance. Recently, Mr. W. L. Roberts provided the senior Mitridatite crystals are deep red to bronzy-red, author with some excellent crystals which afforded pleochroicpale yellow-greento red. Crushedcrystals powder patterns (Table 6) similar to robertsite and and fine-grainedmaterial are dull olive-green,as is practically identical to the powder data of Chukhrov the streak, the latter aiding in distinction from rob- et al. ln addition, minerals D, E, and F from the ertsite whose streak is brown. The specific gravity -+ Borboremapegmatite, described by Murdoch (1955), is 3.24 0.02, determinedby sink-float on single appear to belong to the robertsite-mitridatiteseries. crystals. The prominent powder lines are 8.65/10; 5.ffi/5; Mitridatite commonly occurs at the final stages and 2.74/6. The crystals, which line cavities in of corrosion of primary transition metal phosphates massive material and which are associated with in pegmatites.The dull green stains on silicates in jahnsite, collinsite, hydroxylapatite, and hureaulite, phosphate-bearingpegmatites are in part mitridatite. were collectedon the dumps of the White Elephant Scrapings of such stains afford powder patterns pegmatite,whose paragenesisclosely resemblesthat similar to coarsely crystalline mitridatite but with of the Tip Top pegmatite suite. Single crystals are considerableline broadening. These stains form at thin tabularup to 0.2mm and afforda{100}, c{001} low temperatureand coat large surfacesof pegmatite (small), and rather commonly, ul423l. This last exposuresafter they have been abandonedand ex- form was firmly establishedon the basis of careful posed to weathering.The occurrencesat the Kertch X-ray alignment. Precessionphotographs with a* and Taman peninsulasare in sedimentaxyotilitic horizontal on the films afforded the opportunity to ores.Vivianites, which occur as sedimentarynodules explore b- and c-axisprojections in detail. The single derived from the decompositionof organic remains crystal data in Table 5 thus derived clearly establish as well as vivianitesfrom pegmatites,develop in time T'HREE NEW TR.ANSITION METAL PHOSPHATES 57 a film of mitridatite, suggestingthat ground waters The "mazapilite"of Koenig (1889) was shown by provide Ca2* cations for its formation. Mitridatite Foshag(1937) to be,arseniosiderite. may prove to be a potentially important phasein the Through the help of Mr. John S. White, Jr., we chemistry of soils. Despite the complexity of its secureda specimenof the "mazapilite" and part of crystal cell, we are approachingthe problem of the the material describedby Foshag (1937). The pow- crystal structure with enthusiasm. der data are identical for both and are offered in Table 6 for Foshag'smaterial. The obviousrelation- b. Arsmiosi.derite ship with robertsite and mitridatite provided op- This species,long of uncertain status, occurs at portunity to derive approximate crystal cell data many localities as a low,temperatureoxidation prod- (Table 5) by analogy with those minerals. Koenig uct of liillingite and .In addition, it re- (1889) obtained a specific gravity of 3.58 for places earlier arsenatessuch as . Palache, "mazapilite," and Mrose in Palacheet aI (1951) Berman,and Frondel (1951) list it as hexagonalor obtained3.60. tetragonal,based on optical data. The color is golden yellow in fine massesto reddish-brown in fibers to c. Optical data lor robertsite, mitidatite, and deepreddish or brownish black in granular material. arseniosiderite It is extremelydichroic reddish-brownto practically New optical data for robertsiteand mitridatite plus colorless,according to Larsen and Berman (1934). the data in Larsen and Berman (1934) for arsenio-

TrsI.r 6. Robertsite, Mitridatite, and Arseniosiderite.X-ray Powder Data

ROBERTSITD MITMDATITE MITRTDATITE (Sffiple 2) MTTRIDATITE (SAmpIE 3) ARSENIOSIDERITE (MAPiMi) (Chuldrov g 4., 1958) (Chukhrov et a1., 1958) I/1. q(obs) d(calc) hkJ. I,zI. d(obs) I,/Io d(obs) I,zIo d(obs) I,/I" d(obs) d(catc) hkl t0 8.63 8.63 200 L0 8.64 7 8.8I 6 8.60 I0 8"8q 8.83 200 5 5.61 5.63 03I 6 5.55 I 8 5.60 5 5.62 5.63 03r +.32 +.32 500 3 4.30 3 rr.58 4.54 202 1 4.1|+ 4.13 33I 4 3.28 3.3I 402 2 3.f+8 3.52 4u J_ 3.+9 2 3.1+9 r 3.48 060 rt 3.27 3.25 033 4 3.20 o ? Iq c ? te t+ 3.22 3.2t1 Ii3 3.2+ iaa 5 2.94s 2.945 600 2 3.Lt J.ZU 160 8 2.772 2.760 20tl I 3.03 3.0+ 260 L 3.01 3.02. 2 3.O2 3 2.622 L 2t937 2.952 233 I 2.602 3 2.876 2.877 600 4 2.88r 2.90 2 2.88 2 2.522 t 2.807 2.809 004 L 2.765 t ?uol 2.803 162 z 4.11) 6 2.7+9 2.758 2o+ 7 2.72L ) 7? r0 2.73 + 2.213 2.757 162 I 2.617 L 2.137 + 2.590 2.584 362 t+ 2.562 6 2 q6 6 2.57 2 r.89r 2 2.r+65 2.+59 602 2 2.460 I 2.+6 2 2.+6 r 1 nq7 2 2.223 2.2+9 40q 3 2.207 I L.797 3 2.L60 2.r58 800 r+ 2.169 rr 2.18 5 Z.L7 2 L.770 z.tfz 2 Z.LO6 2.10 3 2.10 4bd l.6r+3 z 2.048 I 2.068 + 20 lines, <2. r.899 3 r.901 3 l.9rt 4 l.9l-9 2 f.745 2 r.7+L 1.750 2 L.7t+5 5 r.623 tl 1.612 7 1.616 7 1.614 I 1.585 I f.588 I.5ttz 3 1.5+8 1.553 3 1.555 I l. r+64 2 I.t+7+ 2 1.r+83 z I. +I2 2 1.q08 1.415 r r.+15 ) 1 ?7q r 1?06 1 1 _772

(II4.6m cffiera dianeter, Fe& radiation, correeted for shrinkage.) 58 PAUL B. MOORE

d. Chemistry of robertsite, mitridatite, and arseniosiderite

We submit two new chemicalanalyses, for robert- site fibers in associationwith singlecrystals from the Tip Top pegmatite and for massivedull green mit- ridatite closely associatedwith crystals from the White Elephant pegmatite. Both afforded powder patternswhich are identical with those from crushed single crystals. The massive green mitridatite con- tained a substantial admixture of quartz which evidently crystallized at low temperatureand which @curs as very small grains in the mass. These Ftc. 4, Pseudo-rhombohedralcrystal of mitridatite resulting analyses,along with analysesfor two rather coarse- from the forms a { 100} and ul42ll. White Elephant pegmatite. Clinographic projection. grainedarseniosiderites reported by Koenig (1889) (: "mazapilite") and Foshag (1937) appear in siderite and those of Chukhrov et al f.or mitridatite Table 8. Ten analysesfor mitridatite from the Soviet are listed in Table 7. We also provide Gladstone- Union appear as a compilation from severalsources Dale calculationsfor all three compoundsand note in Palacheet al (1951). Sinceall specimenswere of the excellent agreement with the o'bservedmean a fine-grained and colloidal nature, they contain indices of refraction. varying amountsof water, a deficiencyof CaO, and All three compounds are optically very similar; an excessof Fe2O3,suggesting mitridatite-goethite- they are strongly birefringent, strongly absorbingin hematite admixtures.Chukhrov et al (1958) offer the Y and Z directions, biaxial negative, and with five new analyses,all rather similar. We provide a list small 2V. The acute bisectrix is roughly pelpen- of the analysesof samples 2 and 3 in Table 8. dicular to the plane of the good { 1@} cleavage.The They proposethe formula CazFeg( POo ) s- ( OH ) *-r,' data of Chukhrov et al (1958) show significantly nH2O. Their study leaves little doubt that our lower indices, doubtless arising from the highly coarselycrystalline material is the same speciesand hydrated nature of their fine-grainedmaterial. that the deviationsin chemicalanalysis, specific grav-

Tenls 7. Robertsite, Mitridatite, and Arseniosiderite.Optical Data

L.77s(s) 1. 78s(5) L.762 1.80 1.815 B,Y 1.82 (1) 1.85 (1) L.770 1.88 1.898 (n> obs 1 .805 1.828 1.870 (n> caLc* 1.803 1.835 1.853

2v t8o t:10' uniaxlal slgn

absorption YrZ >> X YrZ >> X Y,Z >> X YrZ >> X pleochroisrn Y,Z deep red- YrZ deep green- Y,Z dark red- dlsh brown 1sh brown dlsh-brown X pale red- X pale green- X colorless dish-plnk ish yellow orlentatlon x nearly ! {roo} x nearty ! {roo} x ! {roo}

lRobertslte. Ttp Top pegrnatite. zMltridatlte. Whlte Elephant pegnatlte. 3Mltridatit.. Fine-grattred *aieital (Sarqple 2). Chukhrov et aL (L958). qArsenioslderite. Larsen and Berman (1934). They noEe X = c and perfect {001} cleavage. 5ArsenlosiderLte. Larsen and Berman (1934) for tire varlety "nazapilite"

*Fron Gladstone-Dale relationship for ldea1 fornulae. THREE NEW TRANSITION METAL PHOSPHATES 59 ity, and optical propertiesresult from the fine-grained Specimensof the type materials for all three new nature of their material. In addition, three analyses specieswill be depositedin the U.S. National Mu- on fine-grainedarseniosiderite are compiled in Pal- seum. acheet al (1951), but their statusin the absenceof Acknowledgments X-ray patterns is uncertain. Thus, discussionsof them would be of questionablevalue. The electron probe analyses on jahnsite and segelerite, preparation Our two analyseswere computedinto cations per requiring cgreful and choice of standards, were conducted by Mr. T. Solberg. Dr. A. J. Irving kindly unit cell utilizing the specific gravity averagesand contributed to the study when the crystal-chemicalrelation- the cell volumesfrom the X-ray studies.The best ship betweEn overite and segelerite was recognized. Con- agreement,which also agreesremarkably well with tributions bf fragments of type materials from the U.S. the arseniosideriteanalyses, suggests ideal Ca3Mn8.a National Nfuseum were invaluable in providing results on wh.flch could be confounded. Messrs. W. L. (OH)6(HrO)r[POn]n,with Z: 8 for robertsiteand species easily Roberts anil C. Segeler provided samples of many fine speci- obvious isotypy among all three species.We note mens for riesearch. that the massivemitridatites reveal an excessof water This woi'k was supported by the NSF grant GA 10932-Al which is repeatedconsistently in the other analyses awardedto P.B.M. and NSF-MRL support to The University for colloform materials.and subrnit that this excess of Chicago. is adsorbedand not a part of the crystal structure. References In all analyses,the Ca2*content is low by about 5 CuuxHnovJ F. V., Y. A. Morrve, eNo L. P. Enrvrnove to 10 percent.This may resultfrom slightexcesses of (1958) New data concerning mitridatite. Akad. Nauk trivalent cationsand/or alkaliesas substituentsfor S.S.S.R. Ser. Geol. No. 8, 16-26 (translated from the Ca2., but more likely arises from partial vacancies Russian). over the large cation sites. Based on the ideal for- FosHAc, W. F. (1937) and associatedminerals from Mapimi, Mexico. Am. Mineral. 22, 479-484. mulae, the computed densitiesare low by about 5 KoENIG, G. A. (1889) VI. Neue amerikanischeMineral- percent and suggestthat the slight excessesof triva- vorkommen. 1. Mazapilit. Z. Kristallogr. 17' 85-88. lent cations are real. A better fit can be obtained Lenssx, E. S. III (1940) Overite and montgomeryite: two with the formula Ca6Fe3.e(OH) ru(H:O)slPOilr, Z new minerals from Fairfield, Utah. Am. Mineral. 25, = 4, but we doubt whether the preciseformula can 315-326. ,lNo H. BBnueN (1934) The microscopic determi- be unambiguouslystated without knowledge of the nation of the nonopaque minerals, 2nd ed. U.S. Geol. crystal structure. Accordingly, the simpler formulae Suru.Bull. E48, 31. are proposedin this study. Moonn, P. B. (1970) Structural hierarchiesamong minerals The agreementbetween the chemicalanalyses, the containing octahedrally coordinating . l. Stereo- X-ray powderdata, and the opticaldata leaveslittle isomerism among corner-sharing octahedral and tetra- hedral chains. Neues. lahrb. Mineral. Monatsh, 1970, doubt that the three speciesrobertsite, mitridatite, 163-173. and arseniosideritebelong to the samestructure type. - (1973) Pegmatite phosphates: mineralogy and In addition, it is very likely that CagMns.r(OH)e crystal chemistry. Mlneral. Rec. 4, 103-130. (FLO)a[AsO+]rwill prove to be a stablephase and MnosE, M. E. (1955) Problems of the iron- may exist in Nature. phosphates.Geol. Soc. Am. 1955 Program Abstr., 764. Munoocn, J. (1955) Phosphateminerals of the Borborema We concludeby proposingthe following formulae: pegmatites: I-Patrimonio. Am. Mineral. 40' 50-63. Perecnr,, C., H. BrnIvrAN,AND C. FnoNpEr (1951) The * po4]4 robertsite Ca, Mn' nlOH)s(Hro)3 [ System of Mineralo'gy of Dana, Yol. 2, Seventh ed., John Wiley and Sons,Inc., New York, pp. 955-956. mitridatite ca, Fe"n(oH)6(Hro)s I po4]4 Manuscript receioed, JuIy 23, 1973; accepted lor arseniosiderite CarFe'*nlOH)e(Ftrro).[AsOr]r. publication, August 30, 1973'