American Mineralogist, Volume 59, pages 48-59, 1974 l. Jahnsite,Segelerite, and Robertsite,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 Arseniosiderite 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 triphylite-heterosite-ferrisicklerite-rockbridgeite masses, associated with leucophosphite,hureaulite, collinsite, laueite, etc.Type specimensare from the Tip Top pegmatite, 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} cleavage'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, streak 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 minerals 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 PHOSPHATES Following this paragenetic discussion, the crystal a. The aquated oxidaion products of triphylite- chemistry of each speciesshall be discussedsepa- lithiophilite 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 mineral sionally in sufficientabundance, it is difficult to imag- arrd was exposedduring the course of mining 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. purpurite 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 pegmatites 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 todorokite, 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; whitlockite, 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