American Mineralogist, Volume 66, pages 369-375, I98I

Bartonite, a new potassium iron

GENaTO K. CZAMANSKE. RICHARD C. ENN U.S. GeologicalSurvey 345 MiddlSeld Road Menlo Park, Califurnia 94025

B. F. LEONARO U.S. GeologicalSumey Federal Center Denver,Colorado 80225

AND JOAN R. CTENX U.S. GeologicalSumey 345MiddkrteH Road Menlo Park, Califurnia 94025

Abstract

The new mineral bartonite has been found in a mafic, alkalic diatreme at Coyote Peak, Humboldt County, California. Associated v/ith it are the two previously known potassium iron sulfideminsmls, djerfisherite,IQ(Fe,Cu,Ni)24S26C1, and rasvumite,KFerS3, as well as er- dite, NaFe2S3' 2IJ2O,and one or two other new sodium iron sulfide minerals. Bartonite has been found in discrete segregations of sulfide in which pyrrhotite pre- dominates. It is blackish brown, distinctly darker than pyrrhotite on fresh surfaces;in pol- ished section it is yellow, softer and darker than pyrrhotite, and anisotropic. Bartonite is tet- ragonaf l4/mmm, a : 10.424(l),c : 20.626(l)L, Z : 2; density for K5 7eFe21.2aS2ue33.366 g cm-3 (calc.),3.305(10) (meas.). The six strongestlines of the X-ray di.ffractionpowder pattern are (in A;: z.rqtoo;(224),5.99(77Xll2), 1.833(40)(408),9.31(27xl0l)' 3.r39Q7)(3r2)'and 2.379(25)(316).Reflectance in air at 540 nm [s209Vofor Ro, 2l.8Vofor R".. Microindentation hardness(VHN) at l5-gram load is 94-120,mean l(X+9.

Introduction tion in November 1977.'Type specimenswill be de- posited at the National Museum of Natural History, Bartonite, djerfisherite, and rasvumite were noted Smithsonian Institution. in several representativepolished sections of Coyote The geology and mineralogy of the diatreme at Peak material; they defied analysis and identification Coyote Peak have been briefly described by Cza- before we hypothesized that these yellowish green- manskeet al. (1977, 1980). grey sulfide phases might contain potassium. The petrologist name honors Paul B. Barton, Jr., sulfide Occurrence and Paragenesis with the United States Geological Survey, for his Bartonite is typically found associatedwith pyr- outstandingcontributions toward rigorous ulilization rhotite in rare sulflde-rich clots several centimeters of sutfrde mineral chemistry in the deciphering of ore side. Bartonite may oonstituteonly 10-15 per- genesis. Bartonite is the first sulfide mineral for on a which a radiometric ageQ9.4t0.5 m.y.) has been di- I was approved as a new mineral on the rectly determined(Czamanske et a1.,1978).The new Note that bartonite basisof the formula K3Fe1eS1a,and was ascribedthat formula by mineral and the name bartonite were approved by Czamanskeet at., 1978and 1979.More cautiously, it was called "a the Commission on New Minerals and Mineral new K, Fe-sulfide closely related to djerfisherite" by Czamanskeet Names of the International Mineralogical Associa- al.,1980. 0003-004x/8r/0304-0369$02.00 369 CZAMANSKE ET AL; BARTONITE

cent of such masses,but areasseveral mm in dimen- sion may consist of equal portions of bartonite and pyrrhotite. A small amount of pyrite may also be present.Bartonite may be intimately intergrown with the typical silicates--phlogopite,schorlomite, acmite, clinopyroxene, nepheline, natrolite, and sodalite- that comprisethe host rock to the sulfide-rich clots. In many specimens,textures strongly suggestthat bartonite has replacedpyrrhotite (Figs. I through 3). However, it is unclear to what extent bartonite may also have replaced silicate matrix or, indeed, have been replaceditself by late crystallizing silicates.In places, bartonite is finely veined by one or more gangueminerals (Figs. I atd2), and someaggregates Fig. 2. Bright pyrrhotite, interpreted as a residual cuspate of bartonite contain inclusions of phlogopite and island being replacedby bartonite. 77-CYP-31,1.06 x 1.50mm. other gangueminerals. Figures I and,2 show typical bartonite-pyrrhotite replacing pyrrhotite along fractures. It also occurs relations. Bartonite embays pyrrhotite, and minute sparingly as veinlets in bartonite, as enclosuresin veinlets or cusps of the host pyrrhotite project be- gangue minerals that vein bartonite, as fringes of tween individual bartonite grains. Rarely, bartonite minute prisms on bartonite, and as small patchesbe- occursas small skeletalcrystals, as subhedralcores of tween bartonite and pynhotite. Bartonite has par- octahedra,and as atolls in equant in- tially altered to goethiteon one specimen. clusionsof ganguein pyrrhotite. Aggregatesof acicular,high-iron (blades Observationto date has not revealedthe sequen- to 0.5 x 0.02 mm) are present in bartonite in one tial relations of bartonite to the other K and Na sul- sample;analyses show (wt.7o) Fe:24t1, Mn = 1.3, fides--djerfisherite, rasvumite, erdite (NaFeS, . 2H2O), Cd : 1.0.Also presentis a subhedralskeletal crystal .2HrO-as and NaFerS, it has not been seen with of loellingite(0.09 x 0.17mm) senfaining 1.6 wt.Vo them. Ni. Pyrrhotite, typically the dominant sulfide in barto- Small octahedra and platelets of magnetite are nite-bearing assemblages,occurs as irregular masses studdedthroughout someaggregates of bartonite and and occasionallyas tabular crystals.This pyrrhotite appearin someinstances to be localizedat bartonite- contains 47.3 atomic percent Fe (wt.Zo;Fe : pyrrhotite contacts(Fig. 3). Trains of magnetiteocta- : 61.2+0.3,S 39.1+0.3),and X-ray studyshows that hedra are much lessfrequently seenin pyrrhotite. Ti- it is a 5C ordered hexagonalpyrrhotite (Carpenter taniferous magnetite is an irnportant constituent in and Desborough,1964). the host rock, but the fine-grainedmagnetite associ- Pyrite commonly occursas fine-grainedaggregates

Fig. 3. Concentration of sharply bounded, fine-grained Fig. l. Aa irregular remnant of bright pyrrhotite in a matrix of magnetite along itrterface between pyrrhotite (bright) and bartonite veined by silicates.Z7-Cyp-15. 1.3?x 1.94mm. bartonite, 77-CYP-31,0.72x 1.00mrn. CZAMANSKE ET AL.: BARTONITE t7l ated with bartonite and erdite (Czamanske et al., Table 2. Electron microprobe aoalyses of Cl-rich bartonite, phases intermediate to 1979) is nearly free of Ti and is interpreted to be a djerfisherite, rasvumite, and apparently bartonite and djerfisherite. later reactionproduct, perhapspartially in accommo- dation of iron releasedby replacement of pyrrhotite C1-rich barLonile (atomic FelS : 0.899)by bartonite (FelS : 0.762- 0.785).

K r0.5(.2)** 10.6 10.5 10.3 10.4 10.5 Na -l** o.22(.02) o.20 0.20 ComPosition 116.8 Fe 50.3( ,4) 48.7 48,7 \8,2 49.0 Fe-sulfide Ni- 0.25(.03) o.116 0. 43 0.\2 0,011 0, 16 Analysesof bartonite and associatedK, Cu 0.52(.03) 0.66 0.77 0.81 0.93 3.36 phaseswere made on the ARL EMx-sMelectron mi- s 37.3(.6) 38.1 38.2 37.9 38.0 38.0 cL r.35(.05) r.38 r.3o \.23 0,78 0.82 croprobe at Menlo Park, California. (Analytical de- t roo.22 99.90 99.90 99.08 99.35 99.84 tails are noted in the footnote to Table l). Aside from the somewhat more massiveoccurrence and replace- Internediate PhaEes ment relation to pyrrhotite, the strongestindication 12qA q 134 that we were dealing with a phasedistinct from djer- fisherite was in the lower metal-tosulfur ratio char- K r.0.6 r0.5 10.r 9.10 9.15 9.20 9.30 Na 0.64 0.52 o.3q 0,06 - 0.78 0,58 study has shown q4.4 q9.8 acteristic of bartonite. Subsequent Fe \7 .2 \6.7 4?. 1 46.3 A5.7 that this distinction may be uncertain becausebarto- Ni. 0.60 1.30 1.51 0,95 2.37 r.36 0.08 LU 4.q{ 5.12 3.80 7.72 7 ,86 5, 16 2.98 nite compositionappears to vary. 3{. q 35.0 35.4 35.6 35.7 36.3 36.3 0.80 0.79 0.00 0. 00 1. 20 1.02 The compositionof chlorine-poorbartonite is rep- c1 0.95 resented by the five analyses (from two specimens) t 98.83 99.9U 99.04 99.73 99,q8 99.70 r0o.06 averagedin Table l; included is an analysis made on -Eessr.!g. the crystal fragment from which ths 5ingle-crystal 125A r3x 13? 133 data were collected for the structural analysis (Evans

K 9.30 9,2O 9.oo 9.10 9.\5 15.8 Na o.o? 0.76 0.?6 0.04 0.r0 0.02 q5.0 q). Fe \7 .9 trS.q 45.4 \\.2 o Table l. Electron microprobe analysesof Cl-poor bartonite from Ni r. 64 r, 31 1,41 0.87 0.76 0.01 Coyote Peak, Humboldt County, California (weight percent). LU \.92 6.9r. 8.37 9.2r 9.69 0.00 3q.4 34.8 33.8 34.5 33.8 38.6 CI 0.80 1.20 r.26 1.10 r, rJ 0.01 Calculated t 99,58 r00.00 99,90 99.13 r00.04 Bartonite (5)* K5.6gFe29.z7sz6.93rr 99.03

rsample numbers preseneed bo allow insiSht inLo phase K 9.54 (9.44-9.7r) 10.01 association. Na 0.05 (0.02- 0.14) (50.8- 51.8) 51.05 **Indicates esti@ted uncertainty. For each anaLysis 6-8 poi'nts Ni 0.19 (0.r0- 0.31) were occupied for each distinct mineral phase. Co 0.lI (0.07- 0.17) rrr - indicates not sought. Cu 0.62 (0.56- 0.66) s 38.4 (37.6-39.r) 38.94 c1 q.02 (0.0r- 0,02) ----:_ ]00.r3 100.00 D calc. and Clark, l98l). Refinement of site populations in (e/cn31 for Z=2 3.333 3.286 the analysis of the selected crystal fragment gives the formula Kr.urFero.rrSro(S)o'r,in good agreementwith the microprobe analysis of that *lndicates number of discrete areas analyzed (6-8 crystal, (K,Na)r ro(Fe,Ni,Co,Cu)rl.roS* r, (included in poinbs counLed) in specj,mens 15 and 31. IniLiaI values are averages over indicated ranges' Analyses at 15KV and Table l). We believe that chlorine-poor bartonite is 0.02 amp smple current using as slandands: K' bioti.te most abundant. for rasvunite and naLural. Khibina rasvumite for the other K-Fe-S nj-nerals; Na, natural crocidolite; Fe and S' Existence of a chlorine-rich variety of bartonite is synihetic FeS; Ni, synthetic nonosuLfide solid solution postulated on the basis of the data presented in the (mss) conLaininS 9.89 wi.tr Ni; Co, syntheLic mss containing 4.09 wb.i Co; Cu, nabural chalcopyrile; cl, upper pa4 of Table 2. These data representsmall, nalural sodalite. DaLa were corrected by the theorebical indistinguishable areas a few tenths rnm on scheme FRIIME(Yakowibz ef aI.' f973). Identical optically procedunes wene used Lo obLain Lhe data of Table 2. a side, contiguouswith Cl-poor bartonite. The high rrFron content, consideredto be a distinction between slructural analysis by Evans and Clark (1981). sulfur bartonite and djerfisherite, is maintained. Notable, in CZAMANSKE ET AL.: BARTONITE addition to the increasedCl, are the higher content of data for djerfisherite and rasvumite from Coyote K and a distinctly lower summation for Fe + Ni + Peak. The djerfisheriteanalyses are typical of those Cu (seeTable 3). We have been unable to develop a published for other localities (Czamanskeet al., crystal-chemical argument that convincingly explains 1979).The fact that djerfisheriteseems to accommo- this apparentrelation betweencontents of Cl. K and date substantiallymore Ni and Cu than bartonite is Fe + Ni * Cu. As shown in Table 3, compositional probably related to differencesi1[61rling within the data for Cl-bartonite are best matche{ by the for- Fe.S,ocube clustersof the two minerals,despite their mula K-uFeroS2.(So.25CLr5). close structural similarity (Evans and Clark, l98l). The middle row of Table 2 presentsdata for sub- In our experience,rasvumite is the purest K, Fe-sul- stanceswhich appear to be neither bartonite nor fide mineral (Czamanskeet al., 1979).It seemsprob- djerfisherite.All sevenanalyses show more metal and able that the double edge-sharingchains of Fe-S tet- less S than bartonite, and all show significantly more rahedra, characteristic of this orthorhombic mineral Ni + Cu than all but one of the analysesascribed to (Clark and Brown, 1980),are evenless accommodating bartonite. On the other hand, three of the analyses to substitutionsthan the bartonite cube clusters. contain too much K for djerfisherite,two contain no From both a paragenetic and crystal-chemical Cl, and the remaining two have S contentsthat are view, it is interestingto considerwhat factors might well above those expectedfor djerfisherite.We ofer control crystallizationof the three K,Fe-sulfide min- two suggestions,which ditrer chiefly in scale:(l) per- erals, djerfisherite, bartonite, and rasvumite. The haps the individual, close-packedlayer stackingstyp- most obvious clue is in the apparent oxidation state ical of bartonite and djerfisherite (Evans and Clark, of Fe. Assumingthat all S is 2-, iron is fully reduced 1981,Fig. 1) are intermingled in hybrid fashion; or in djerfisherite,has a valence of 2.50 in rasvumite, (2) perhaps the phases are intergrown on a sub- and in bartonite has a formal valence of 2.27 n microscopicscale. In contrastto bartonite, which oc- KrrFe",rSru.,and 2.36 n KoFeroSro,(SozrCLrr).The curs in substantialmasses with millialsters of conti- structuresand occurrenceof theseminerals may thus nuity, djerfisherite and these possible intermediate reflect the oxidizing potential in the environment in substancesoccur as fine, interstitial disseminations which they forrred. This explanationfits reasonably amid silicatesor as thin "skins" on late "pegmatitic" well with the occurrenceof these phasesat Coyote silicate crystals (e.g., phlogopite). Thus, there has Peak.The common occurrenceof djerfisheriteas dis- bgen no opportunity to conduct comparativesingle- seminated fine grains amid silicates suggestsearly crystal studiesof thesephases. crystallization, whereasbartonite occurs in replace- The lower part of Table 2 presentscomparative ment relation to earlier pyrrhotite. In contrast,bun- dles of rasvumite needles(Czamanske et al., 1978\ typically occur in small pegmatiticclots that seemto Table 3. Average Cl-rich bartonite composition compared to have formed at a late stage.Rasvumite is associated ,h".-tt."l f...rt"". with the Na,Fe-sulfidephases in which iron is also fully oxidized,and erdite replacesdjerfisherite. Cl-nich K6F"?OSZ6/ K6F.ZOSZ6lK6FuZtSz6/ From perspective, barLoniLer(So.zlCro.z:) (s0.5cl0.5) (SO.e5clo.7t) another it could be said that the K,Fe- sulfide minerals suggest an oxidizing trend during consolidationof the Coyote Peak diatreme. K 10.46 ro.57 10.57 10.30 Na 0.2I Chemical properties Fe 48.98 50.32 50.34 5r.54 Ni 0.32 Bartonite is readily soluble with effervescencein Cu 0. 7tt s 37.90 37.9r 38.29 36,93 hot concentratedHNO, and soluble with difficulty ua L. zL 1.20 0.80 r. r7 and effervescencein hot concentratedHCl. When L 99.82 100.00 100.00 100.00 heated in a closedtube, it gives off sulfur and turns black. Its initial decompositionproduct pyrrhotite; D ca1c, is 8/cn3 with continued heating in a platinum crucible, it is for Z=2 oxidized to hematite. 3.283 3.289 3.288 3.372

*Aue".g" Crystallography excludes the single hlgh-Cu barlonite (?) analysis of Table 2. Unit-cell dimensions were deterrrined from pre- cessionphotographs (Zr-filtercd Mo radiation) of the CZAMANSKE ET AL.: BARTONITE 373 hkO,0kl, hhl, and hkl nets.Extinctions in thesepho- Table 5. X-ray powder diffraction data for bartonite, Coyote Peak" tographslead to the difraction aspectI/4***' crystal Humboldt County, California structure study (Evans and Clark, l98l) shows the cal cu lated* Observed** ^ ghkg (i) space group to be l4/mmm. The cell dimensions hk0 (i) I r Elks given in Table 4 were refined by least-squaresanaly- 002 10.313 16 15 10.31 sis of the X-ray powder data using the computer pro- l0r 9 .303 68 27 9.3r tI0 7.37r 12 8 7.38 gram of Appleman and Evans (1973).Calculated in- 112 5.997 58 71 5.99 tensities obtained from the crystal structure study of 103 7 8 5.74 Evans and Clark are given in Table 5 and have been 105 J. dJO 006 3.438 4 usedto index the data. 301 3.426 15 12 3.428 310 3.296 9 15 3,296 The X-ray powder diffraction data (Table 5) are 3r2 3. r40 32 27 3. r39 similar to thoseof djerfisherite(Fuchs, 1966; Genkin 116 3,115 14 l5 3.tt6 et al., 1969)but may easily be distinguishedby the 303 3. 10t l0 3. 102 2.998 100 t00 2.998 1 presenceof additional lines, the strongestof which 206 2.870 8 2.863 areat 9.31,3.139,2.389,2.374, and 1.833A. 321 2.853 4 Bartonite typically occurs as anhedral masses.A 107 2.835 9 6 2.837 4ll 2.509 2.510 few single crystals are present in patches of fine- 2.390 l8 17 2.389 315 , 17q 40 25 2.379 grained silicate matrix and as parallel intergrowths 406 2.077 2 8 2,075 with coarseacmite. The crystals, lessthan 5 pm wide 431,501 2.074 l0 long, prisms, 5t2 2.005 8 5 2.000 and 5 to times as are some of them t.999 1 terminated at one end by a pyramid or by a pyramid 11.10 r. 985 i.987 435,505 r ,861 4'1 4 1,860 and the basal pinacoid. The opposite ends of these 440 r.843 41 I .841 408 1.833 79 I .833 prisms are gently curved or ragged.The form I 12] was identified on an exceptional crystal fragment. 532 1.761 4 516 1,.757 4 3 431 1,702 8 1.698 Physicalproperties 419 r .698 3 624 1,570 I4 t2 1.570

Bartonite occurs as blackish-brown anhedral 22.t2 1.558 6 4 1,551 masseswith a submetallicluster and a black streak. 7t2 1.459 4 2 r.459 800 r.303 9 2 1.302 It has a conchoidal fracture. In polished sections a 00.l6 1,289 4 2 1.288 1.272 2 r.272 was noted distinct cleavage {ll2} on some sections *c€lculated spacings listed for lhkg >5.5008. Indices fr@ lying parallel to the prism axesof rare microcrystals. Ieast-squeres analysis of X-ray powde! deta using the progrm of

Applehan and Evans (1973). Calculated intensities fr@ comPuter progran PowDER (I. c. Jahanbagloo, unpubl. 1954' revised 1969' coordinates Table 4. Unit-cell data for bartonite Univ. Rochester, New Yotk) using prelininary at@ic = (Evans and Clark, 1980), and intensities nomalized witir. (224)

100. Space Group I4lIrm **Specimen No. 77-cYP-15' X-ray diffractoeter conditions are: = chart no. X-4309; Cu/Ni radiationl ICuKdr 1.5405988;6i1icon

used as internal scandard; scanned at l/4o Dinute frm 4-800 20. a (fr) 10.424(r) 20.626(r)

v

good polish, but at a magnificationof l50X someex- Table 6. Reflectance of groups of bartonite grains, measured at tremely fine scratchesare visible. The polishing hard- standard wavelengths. ness is much less than that of pyrrhotite. narr tr Bartonite is weakly magnetic(somewhat less mag- , ilmenite) netic than and may easily be distinguished 470 589 650 nn by this property from the associated pyrrhotite, C1-poor which is much more strongly magnetic. Its specific (3 graj.ns) gtavity (3.305;Table 4) aids in distinguishingit from R, range 20.2-21.9 25.2-29.0 24.8-28,0 22,7-25.6 &l = RO*t 20'8+0.8 27.3!I.9 25.9!L,7 2\.2!I.3 djerfisherite, which has a specific gravity of about Rr* 20.9+0.7 27.5+L6 26.0+I.4 24.4+1 .I 3.9. R2-Rg,mx. 0.3 0.6 0.5 o.7 Unanalyzed Optical properties (U grains) In polished section, bartonite aggregatesisolated R, range I8,2-22.o 2r.3-28,5 22.5-28.2 2\.0-25.\ fu = Ro 19.q+r.5 23.2+3.0 2\.1+2,2 2\.6+0,7 by the field diaphragm are yellow, neither bright nor R 19'8+l'tl 23.7+2.8 2\.6+2.1 24.9+0.8 R2-Rt, mx. 1. 3 1.4 r.o f.) dark according to BFL, and appear brownish yellow

to GKC. Reflection pleochroism is barely per- rReflectance measured by B. F. Leonard with a Zeiss MPM micro- photometer fitted with a Soith verti.cal illuoinator and a Veril ceptible. Anisotropism is distinct, al-most without type-S running inLerference filter whose half-width at tint. Internal reflectionis absent.Extinction is paral- half-hej.ghb is 110 nn. objective I6x PoI, N.A, 0.35. Zei-ss-calj.brated SiC standard no. 052. Hounts press-leveled on lel to the prism edge.Against pyrrhotite, bartonite is plasticine. Final polish wibh 0.05-lrn alunina in Eter on Buehler nicrocloth. ReproducibiliLy of individual neasuremeots yellowish green gray, or yellowish green brown, at is +1t rel.atj.vely. glance first resembling greenish members of the ten- **Mean and standard deviation s. nantite-tetrahedrite seriesbut somewhat darker than these and much darker than pyrrhotite. Against py- rite, bartonite is slightly greenish yellow and much tance measurementsmade at 400-500 nn on addi- darker. In oil, isolated aggregatesof bartonite seem tional bireflecting grains differ somewhat in absolute little changed,but bartonite next to pyrrhotite ap- values of Ro and RE, but confirm the presence of pears greenish gray or greenish brown and much crosseddispersion in the blue. The phenomenonof darker. In a maritime climate, bartonite shows no crossed dispersion of reflectance (equivalent in uni- tarnish months after polishing. The reflectanceof two groups of bartonite grains is Table 7. Reflectance of two bartonite grains, measured at 20-nm given in Table 6. Substantial differences in reflec- intervals. (Measured on two separate grains, one isotropig the other anisotropic. Rq of both grains identical at standard tance behavior are evident from grain to grain within waverengthst ttl"l1l;ti3;,lll Forconditions or the two groups. How much of the difference is due to fr"t,H; slight variation in composition and how much to the vagaries of polishing and measuring, we do not D--_ d " tP know. For some bartonite grains, the reflectance is Wavelength, nm D-DD-DI higher in the middle of the spectrum than at 470 and AUlL 650 nm; for other grains, reflectanceincreases with increasingwavelength, or increasesfrom 470 to 589 400 ?L.7 IO. J t420 L6.7 I4.4 nm and then remains constant. Becausea selection of 440 L7.7 L7.2 good crystals of known orientation is not available, 460 18.4 18.6 we do not know if the few highly bireflecting grains 480 t9.4 19.5 are aberrant or if they more nearly representthe true 500 L9.7 20.6 bireflectanceof the mineral. 520 20.3 540 zo.9 tL.o Two grains of bartonite were used for measure- ments of Ro and R" throughout the visible 560 2L.9 22.7 spectrum 580 zz.7 23.2 (Table 7). These grains were chosen becausethey 600 23.4 23.7 were best polished, not becausethey showed the 620 23.9 2\.3 highestbireflectance. The bartonite grains of Table 7 640 25.L are optically positive throughout most of the spec- 660 z5.o 25.5 680 25.2 26.L trum, but they are optically negativeat wavelengths 700 26.\ zo.> below 455 nm. At 455 nm, they are isotropic. Reflec- CZAMANSKE ET AL.: BARTONITE

Table 8. Quantitative color designation of bartonite referred to ten in the 50G-540nm region. Therefore, the eye I.C.L illuminant C. (Method of 30 selectedordinates.) focusedon bartonite adjacentto pyrrhotite seesgreen or yellowish green,not yellow. The effectis enhanced hrnm Pe, P becausebartonite has the greater excitation purity; that is, regardlessof the hue sensedby the observer, R6 0.333 2L.7 58r. LI.2 the saturation is intrinsically greaterfor bartonite. RE' n ? ?q 0.342 577 rJ.o

Acknowledgments axial substancesto changeof optic sign) is common The counselofHoward T. Evans,Jr. has been especiallyvalu- among ore minerals, though it has seldom been re- able to us throughout this study. We also thank him, Priestley ported for minerals of low bireflectance. Toulmin III, A. J. Criddle, and J. Chisholrnfor perceptivereviews Provisional values of n and /c for the anisotropic of the manuscript. grain of Table 7 were obtained by calculation from References measurementsof R"i' and R"i' againstthe calibrated : : Appleman, D. E. and Evans,H. T., Jr. (1973) Iob 9214:Indexing SiC standard.At 589 nm, Rq 23.3s,Re, 23.7Voin least-squaresrefinement of powder diffraction data. U.S. Na- air;Ro: 11.3,RE,: ll.6vonotlat24.6oC.Thus, no tional Technical Information Service,Document PB-216 188. : 2.22,/ro : 1.10,nE' : 2.22r,kE' : 1.12.The oil Carpenter,R. H. and Desborougb,G. A. (1964)Range in solid so- used was Cargille D/N 58.884;n"" (589) : Iution and structure of naturally occurring and pyrrho- l.515l+0.0002,independently determined by Ray E. tite. American Mineralogist,49, 1350-1365. Clark, J. R. and Brown, G. E. (1980) Crystal structue of rasw- Wilcox, U.S. Geological Survey. Becausesmall er- mite, KFe2S3.American Mineralogist, 65, 477482. rors in the measurementof reflectancesubstantially Czamanske,G. K., Erd, R. C., Sokolova,M. N., Dobrovol'skaya affect the calculatedvalues of z and k, we emphasize M. G., and Dmitrieva, M. T. (1979)New data for rasvumiteand that the valuesgiven for the singlebartonite grain are djerfisherite.American Mineralogist, 64, 776-778. Erd, R. and Blake, M. provisional. Note that the valuescited for R"i'in this Czamanske,G. K., Lanphere,M. A., C., C., Jr. (1978)Age measurementsof potassium-bearingsulfide min- paragraph were obtained by remeasurement,not by erals by the Af /Afe technique. Earth and Planetary Science interpolation from Table 7. Therefore, R'i'is validly Letters,40,107-110. paired with R'il in deriving n and /c. To produce a Czamanske,G. K., Leonard,B. F., and Clark, J. R. (1980)Erdite, valid set of measurementssome tine after obtaining a new hydrated sodium iron sulfide mineral. American Mineral- ogist,65, 509-515. the data of Table 7, it was necessaryto repolish the Czamanske,G. K., Meyer, C. 8., Erd, R. C., and Norman, M. B., specimen,retrieve the grain needed,remeasure R"i', ll (1977\ The Coyote Peak diatreme, Humboldt County, Cali- and immediatelymeasure R"il. Such a precautioncan fornia. (abstr.).EOS, 58, 1247. control some of the variables that enter in to the Evans, H. T., Jr. and Clark, J. R. (1981)The crystal structure of measurementof reflectance,but it cannot ensure that bartonite, a potassium iron sulfide, and its relationship to the pentlandites values structures of and djerfisherites. American Mineral- the derivative n and k are correct. ogist, 66, 376-384. Quantitativecolor data calculatedfor the bartonite Fuchs,L. H. (1966)Djerfisherite, alkali copper-ironsulfide: a new grains of Table 7 are given in Table 8. These data, mineral from chondrites. Science, 153, 166-167. derived from microphotometry and selectively in- Genkin, A. D., Troneva, N. Y., and Zhuravlev, N. N. (1969)The tegrated over the visible spectmm, define a yellow of first occurrence in ores of the sulfide of potassium, iron, and Geologii Rudnykh Mestorozhdenii, 11, rather low brightnessand low excitation purity. The copper--djerfisherite. No. 5, 57-64. color definition agrees fully with BFL's visual im- Henry, N. F. M. (Ed.) (1977)rM^/cou Quantitativedata frle. In- pressionof the color of isolatablegrains of bartonite: ternational Mineralogical Association,Committee on Ore Mi- yellow, neither bright nor dark. croscopy, London. The observation that bartonite looks yellowish Vyal'sov, L. N. (1973) Spektry otrazheniya rudnykh mineralov Moskva,Akademiia Nauk green pyrrhotite [Reflectancespectra of ore minerals]. against can be explained by refer- SSSR, Institut Geologii Rudnykh Mestorozhdenii,Petrografii, ring to the reflectanoe curves of the two minerals. Mineralogii i Geokhimii. Curves for hexagonalpyrrhotite can be plotted from Yakowitz, H., Myklebust, R. L., and Heinrich, K. F. J. (1973) reflectancesmeasured by K. v. Gehlen and H. Piller FRAME:An on-linc correction procedure for quantitative elec- (Henry, 1977, card no. 1.7240.2ior by Vyal'sov, tron probe analysis.U.S. National BureauofStandards Techni- cal Note 796. 1973).When the curvesof the two minerals are com- pared, it is evident that the reflectancecurves ofbar- Manuscript received,July 7, 1980; tonite, relative to those ofhexagonal pyrrhotite, flat- acceptedforpublication, October 22, 1980.