DOCSLIB.ORG

The Identification of Fe2+ in the M(4) Site of Calcic Amphibores

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Identification of Fe2+ in the M(4) Site of Calcic Amphibores American Mineralogist, Volume 62, pages 205-216, l9Z7 The identificationof Fe2+in the M(4) siteof calcicamphibores DoN S. GoloueN e.NoGroncn R. RosslleN Diuision of Geological and planetary Sciences Califurnia Institute of Technology Pasadena,Califurnia 9 I I 25 Abstract Evidenceis presentedfor the occurrenceof Fe2+in the predominantlyCa-filled M(4) siteof calcicamphiboles. Absorption bands in theelectronic spectra at 1030nm in p andat2470 in a providea sensitivemeans for identifyingFe2+ in thissite. The large e valuefor the 1030band, the largeenergy separation between both bands,and the similarityto the spectraof Fe2+in large,highly distortedcoordination sites in other mineralsprovide the basisfor theM(4) site assignment.The energysplittings and polarizationanisotropy of thesebands are analyzed, using a point-chargemodel basedon Cru symmetry.Spectral data indicatethat the Fe,+ contentin the M(4) site variessignificantly among the calcicamphiboles. Introduction Fe2+in tetrahedralcoordination, also in a spectrum .Little is known about the Fe2+content of the M(4) of actinolite.Both ofthese bands occur in the spectra si{eof calcicamphiboles. M(4) Fe2+has beendifficult of the orthorhombic amphiboles of the anthophyl; to identify becausecalcium generallyoccupies 85-95 lite-gedriteseries, (M g,Fe,Al),(Si,Al).O,,(OH)z; how- (1974) percent of this site (Leake, 1968);therefore, only a ever, Mao and Seifert assignedboth bands small percentageof the total iron in most samplescan to Fe2+in the M(4) site. occupy the M(4) site. Hence, it is difficult to analyze The high degreeof distortion of the M(4) site is for M(4) Fe2+in the complex Mdssbauerspectra, and expectedto producelarge crystal-field splittings anal- to detectsmall quantitiesof Fe2+in a predominantly ogousto the spectraof Fe2+in the distortedM(2) site Ca-filled M(4) site by crystallographicanalysis. The of orthopyroxene, (Mg,Fe)rSirO.. Burns (1970), purpose of this paper is to identify Fe2+in the M(4) Runcimanet al.,(1973),and Goldman and Rossman site with electronic absorption spectra and to show (1976, 1977) studied a variety of orthopyroxenesin that this techniqueis sensitiveto small concentrations which bands at about 930 nm and 1850nm were of Fe2+in this site. assignedto transitionsto excitedstates derived from uE, The electronicabsorption spectra of the calcicam- the splitting of the octahedral state.These inter- phiboles consist of a superposition of absorption pretations provide a basis for the analysis of the bands that arise from ferrous iron in several sites of calcic amphibole spectra.A third absorption band at different coordination geometries.Amphiboles con- 2350cm-' was identifiedin orthopyroxene(Goldman tain three sites M(l), M(2), and M(3) that more and Rossman, 1976) and assignedto a transition uT"r(On) closely resembleregular octahedra than the fourth within the split stateof Fe2+in the M(2) site. site,M(4), which is highly distorted from octahedral We have examinedpolarized spectrato seeif a sim- geometry. Fe2+in the M(4) site of calcic amphiboles ilar band arising from Fe2+inthe M(4) site occursin has not been previously identified in absorption the 1200-4000cm-' region. spectra.Burns (1970)presented absorption spectra of two actinolites, Car(Mg,Fe)uSirOrr(OH)r, in the Sample description 350-1500nm region in which all Fer+ featureswere Tremolite: Mt. Bity, Malagasy Republic (Lacroix, attributed to Fe2+in the M(l), M(2), and M(3) sites. l9l0); CIT #8038;a2 cm prismatic,euhedral crystal It can be inferred from this discussion and from that is green,transparent, and free of inclusions.Mi- Burns (1965)that the main band at about 1035nm croprobe analysesof various chips from the crystal arisesfrom Fe2+in the M(2) site. White and Keester show a range of iron content from 1.6 to 2.8 weight (1966)assigned a band in the 2300-2500nm regionto percent FeO, but the microprobe analysis of the 205 GOLDMAN AND ROSSMAN CALCIC AMPHIBOLES sampleused for opticalspectra indicated 2.06 percent Test-e l. Microprobe analYses FeO (Table l) and the wet chemicalanalysis of the Mdssbauersample indicated 2.09 percent FeO. Weig percent of oxides Si02 57,65 57.01 42,9L Actinolite:Zillerthal, Tyrol, Austria; CIT .88 #4916; Ti0 2 .07 1.06 12.69 dark green,prismatic, euhedral laths up to l5 mm A120 3 1,31 Cr203 .24 long and up to 4 mm acrossthe basalsection in a Mco 23.62 2L.36 14.44 MnO ,22 .09 talc-mica schist.The absorptionspectra were taken I'eO 2.06 5.72 10.25 in areason the orientedslabs that were free of mi- Ca0 L3.42 12,30 13.00 Na20 .6r .4L caceousinclusions common to thesesamples. The Kzo .20 .05 r.57 F .2L .06 !.66 microprobeanalysis (Table l) is similarto thosere- c1 .04 in Leake 99.L9 98.43 99.94 ported for actinolitesfrom this locality ,09 .03 .70 (1e68). .01 99.O9 98.40 99.24 Pargasite:Pargas, Finland; CIT #2573;large crys- Formul a Proportionsx crystalsare black, Si 7.8r 7.87 6.28 tal clustersin whichthe individual A1(rV) to .13 t,72 along(010), and haveother well-developed (vr) .04'l .t+11 tabular A1 ,.021 -- | +. t | 4.40 | :.rs crystalfaces. These crystals occur in marbleand com- | I Ti .01 | -l .10 5.16 | monly havecalcite inclusions. The spectrawere ob- Cr - | ''"' ne F -l I Mn .03 | .01| tained in inclusion-freeareas. The compositionof .23J .66J L.26J this samplediffers from thosereported for other par- L.95 1R? 2,03 Na .11 .69 gasitesfrom this localityin Leake(1968) in having .01 higherFe and lower F and Al. Theseminerals did not showchemical zonation in 3. Pargaslte, Pargas, Finland the areain which the opticalspectra were taken on *The formula proportlons are obtained by nomallztng the total- posltive io 46 assuming all Fe ls Fe2*' the (100)slabs. "t..i. Experimentalmethods All spectraldata presentedin this paperhave been the two components of each doublet were con- obtained at room temperatureon self-supportingstrained to be equal, although the half-widths of the (010)and (100) slabs. The method of preparationand different doublets were allowed to vary. Due to the data analysishave been described(Goldman and small percentageof Fe8+in this sample,the position Rossman.1977). of peak C was fixed, the areas of C and C' were The M<jssbauerspectrum was obtainedat room constrained to be equal, and their half-widths were temperatureusing a MCA unit drivenby a conven- specified.The sinusoidalvariation of the background tional loudspeakerdrive system with moving-source was also fitted. The resultingparameters are given in geometry.A l6 mcu?Co source in a palladiummatrix Table 2. A 12 value for the 200 channelsanalyzed is wasused, which produced a minimumline width of 196. 0.27 mm/sec.The velocityincrement was approxi- The electron microprobe analyses(Table I ) of the mately0.04 mm/sec/channel and was calibrated with three amphiboleshave beenobtained within the areas laboratorystandards. The sampleconcentration was in which the optical spectra were obtained on the approximatelyI mg Fe/cmz.The samplewas ground (100) slabs.The analysesof the Mt. Bity andZiller- under acetone,meshed to obtain a grain sizefrom thal sampleswere normalized to chargeassuming 23 43-74 p.m and set in lacquerin the bottom of a shallow l" diameterplastic dish. Nearly 3 X ltr countsper channelwere accumulated, and the spec- Tnsls 2. MdssbauerParameters trum was analyzedusing the computer program (W. Dollase,personal communication). ISOMER* QUADRUPOLE Mosrr A. PEAKS SHIFT SPLITTING HALF-WIDTH % AREA Other experimentaldetails are similar to Dollase (1973). )+ Mr Fe- l.l4 2.82 .32 5L.4 (!0 .92) The Mdssbauerspectrum of the Mt. Bity tremolite )+ BB' !e L,\t 1.84 .34 4r.4(!r.22) peakswhich included two quad- ?+ wasanalyzed for six cc' Fe' 0.48 .53 7.2(!t.2O) rupoledoublets from Fe2+(AA', BB') andone quad- *Relative rupoledoublet from Fe3+(CC'). The half-widthsfor Eo Feo ln m/sec GOLDMAN AND ROSSMAN: CALCIC AMPHIB7LES oxygensand that all Fe is Fe2+.Mdssbauer data (Papikeet al., 1969)with the principaldistortions presentedin this paperfor the Mt. Bity sampleand being due to (l) an elongationof the Fer+-O(6) the analysesgiven in Leake(1968) for actinolites bondswith a reductionin the O(6)-Fc,+-O(6)bond from the Zillerthal area indicate that less than l0 angle;(2) a twistingof the 0(6)-0(6) bond aboutb percentof the total Fe is Fe3+.Using an Fes+/Fe relativeto the O(2)-O(2)bond; (3) a relativecom- ratio of 0.l0 doesnot changethese formula propor- pressionof the Fe'+-O(4)bonds; and (4) a removal tions.The formulaproportions for thePargas sample of the centorof symmetry.The grune'ite M(4) site havebeen obtained similarly. Changing the Fes+/Fe will be used as the structuralmodel to analyzethe ratio up to 0.30 does not appreciablychange the bandsdue to Fe2+in theM(4) siteof actinolite.This resultingformula proportions. The sum of AlvI, Fe. assumesthat Fe2+occupies a "gruneriteposition" in Mg, Ti, and Mn is closeto 5.0,and the sumof Ca,K, the actinoliteM(4) site. and Na is approximately3.0 with Fe8+/Feratios of lessthan 0.30. Descriptionof spectra The spectraof the Mt. Bity tremoliteare presented Crystalstructure in Figure3 to illustratethe featuresthat characterize Calcic amphibolesare monoclinic with space most calcic amphibolespectra, These spectra will group Cr,*. The M(l), M(2), and M(4) siteshave serveas a basisfor theidentification, assignment, and point-group symmetry Cr, and the M(3) site has crystal-fieldanalysis of the absorptionbands due to point-groupsymmetry Crx. Fe2+in theM(4) site.Many of the featuresshown in The structuraldifferences between the M(l), M(2), and M(3) sites and the M(4) site suggestthat the spectroscopicfeatures of ferrous iron in thesesites csinP c will markedlydiffer. The (c*-6) and (a-c) Onrrp az"i (Johnson,1965) projections of the M(l), M(2), and M(3) sitesof actinoliteare presentedin Figure l.
Load more

Recommended publications
  • Chemographic Exploration of Amphibole Assemblages from Central Massachusetts and Southwestern New Hampshire
    Mineral. Soc. Amer, Spec. Pap. 2, 251-274 (1969). CHEMOGRAPHIC EXPLORATION OF AMPHIBOLE ASSEMBLAGES FROM CENTRAL MASSACHUSETTS AND SOUTHWESTERN NEW HAMPSHIRE PETER ROBINSON AND HOWARD W. JAFFE Department of Geology, University of Massachusetts, Amherst, Massachusetts 01002 ABSTRACT Fourteen wet chemical and forty electron-probe analyses were made of amphiboles from critical assemblages in the kyanite and sillimanite zones of central Massachusetts and southwestern New Hampshire. The rocks studied in- clude plagioclase amphibolites that are metamorphosed mafic lavas and tuffs, aluminous anthophyllite rocks of uncertain derivation, quartz-garnet-amphibole granulites that are metamorphosed ferruginous cherts, and pods of ultramafic amphibolite. The rocks contain the following associations: hornblende-anthophyllite, hornblende-cummingtonite, anthophyllite-cummingtonite, hornblende-anthophyllite-cummingtonite, anthophyllite-cordierite, and anthophyllite- kyanite-sillimanite-staurolite_garnet. The following generalizations are made: 1) The cummingtonites are compositionally simple, containing neither sig- nificant AI/AI, NaJAI, nor Ca substitution. 2) The hornblendes are high in AI/AI substitution. Those coexisting with cummingtonite in the kyanite zone or in retrograded rocks have a higher Al content than those coexisting with cum- mingtonite in the sillimanite zone, in close agreement with the prograde reaction tschermakitic hornblende -7 cumming- tonite + plagioclase + H20 proposed by Shido. The Na content of hornblende is considerably less than that of the theoretical edenite end member and is relatively insensitive to variation in the Na content of coexisting plagioclase. 3) Anthophyllites coexisting with hornblende contain about 1as much AI/AI substitution and 1as much Na substitution as coexisting hornblendes. Ca is negligible. Anthophyllites with cordierite, aluminosilicates, or garnet equal or surpass hornblende in AI/AI and Na substitution.
    [Show full text]
  • Optical Properties of Common Rock-Forming Minerals
    AppendixA __________ Optical Properties of Common Rock-Forming Minerals 325 Optical Properties of Common Rock-Forming Minerals J. B. Lyons, S. A. Morse, and R. E. Stoiber Distinguishing Characteristics Chemical XI. System and Indices Birefringence "Characteristically parallel, but Mineral Composition Best Cleavage Sign,2V and Relief and Color see Fig. 13-3. A. High Positive Relief Zircon ZrSiO. Tet. (+) 111=1.940 High biref. Small euhedral grains show (.055) parallel" extinction; may cause pleochroic haloes if enclosed in other minerals Sphene CaTiSiOs Mon. (110) (+) 30-50 13=1.895 High biref. Wedge-shaped grains; may (Titanite) to 1.935 (0.108-.135) show (110) cleavage or (100) Often or (221) parting; ZI\c=51 0; brownish in very high relief; r>v extreme. color CtJI\) 0) Gamet AsB2(SiO.la where Iso. High Grandite often Very pale pink commonest A = R2+ and B = RS + 1.7-1.9 weakly color; inclusions common. birefracting. Indices vary widely with composition. Crystals often euhedraL Uvarovite green, very rare. Staurolite H2FeAI.Si2O'2 Orth. (010) (+) 2V = 87 13=1.750 Low biref. Pleochroic colorless to golden (approximately) (.012) yellow; one good cleavage; twins cruciform or oblique; metamorphic. Olivine Series Mg2SiO. Orth. (+) 2V=85 13=1.651 High biref. Colorless (Fo) to yellow or pale to to (.035) brown (Fa); high relief. Fe2SiO. Orth. (-) 2V=47 13=1.865 High biref. Shagreen (mottled) surface; (.051) often cracked and altered to %II - serpentine. Poor (010) and (100) cleavages. Extinction par- ~ ~ alleL" l~4~ Tourmaline Na(Mg,Fe,Mn,Li,Alk Hex. (-) 111=1.636 Mod. biref.
    [Show full text]
  • List of Abbreviations
    List of Abbreviations Ab albite Cbz chabazite Fa fayalite Acm acmite Cc chalcocite Fac ferroactinolite Act actinolite Ccl chrysocolla Fcp ferrocarpholite Adr andradite Ccn cancrinite Fed ferroedenite Agt aegirine-augite Ccp chalcopyrite Flt fluorite Ak akermanite Cel celadonite Fo forsterite Alm almandine Cen clinoenstatite Fpa ferropargasite Aln allanite Cfs clinoferrosilite Fs ferrosilite ( ortho) Als aluminosilicate Chl chlorite Fst fassite Am amphibole Chn chondrodite Fts ferrotscher- An anorthite Chr chromite makite And andalusite Chu clinohumite Gbs gibbsite Anh anhydrite Cld chloritoid Ged gedrite Ank ankerite Cls celestite Gh gehlenite Anl analcite Cp carpholite Gln glaucophane Ann annite Cpx Ca clinopyroxene Glt glauconite Ant anatase Crd cordierite Gn galena Ap apatite ern carnegieite Gp gypsum Apo apophyllite Crn corundum Gr graphite Apy arsenopyrite Crs cristroballite Grs grossular Arf arfvedsonite Cs coesite Grt garnet Arg aragonite Cst cassiterite Gru grunerite Atg antigorite Ctl chrysotile Gt goethite Ath anthophyllite Cum cummingtonite Hbl hornblende Aug augite Cv covellite He hercynite Ax axinite Czo clinozoisite Hd hedenbergite Bhm boehmite Dg diginite Hem hematite Bn bornite Di diopside Hl halite Brc brucite Dia diamond Hs hastingsite Brk brookite Dol dolomite Hu humite Brl beryl Drv dravite Hul heulandite Brt barite Dsp diaspore Hyn haiiyne Bst bustamite Eck eckermannite Ill illite Bt biotite Ed edenite Ilm ilmenite Cal calcite Elb elbaite Jd jadeite Cam Ca clinoamphi- En enstatite ( ortho) Jh johannsenite bole Ep epidote
    [Show full text]
  • The Effects of Composition Upon the High-Pressure Behaviour of Amphiboles: Compression of Gedrite to 7 Gpa and a Comparison with Anthophyllite and Proto-Amphibole
    Mineralogical Magazine, August 2012, Vol. 76(4), pp. 987–995 The effects of composition upon the high-pressure behaviour of amphiboles: compression of gedrite to 7 GPa and a comparison with anthophyllite and proto-amphibole 1,2, 1 3 4 F. NESTOLA *, D. PASQUAL ,M.D.WELCH AND R. OBERTI 1 Dipartimento di Geoscienze, Universita`di Padova, via Gradenigo 6, 35131 Padova, Italy 2 CNR Istituto di Geoscienze e Georisorse, UOS Padova, via Gradenigo 6, 35131 Padova, Italy 3 Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK 4 CNR Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, 27100 Pavia, Italy [Received 10 February 2012; Accepted 23 March 2012; Associate Editor: G. Diego Gatta] ABSTRACT A single-crystal X-ray diffraction study of a sample of natural gedrite from North Carolina, USA, with A B 2+ C 2+ 4+ the crystal-chemical formula Na0.47 (Na0.03Mg0.97Fe0.94Mn0.02Ca0.04) (Mg3.52Fe0.28Al1.15Ti0.05) T W (Si6.31Al1.69)O22 (OH)2, up to a maximum pressure of 7 GPa, revealed the following bulk and axial moduli and their pressure derivatives: K0T = 91.2(6) GPa [K0T’ = 6.3(2)]; K0T(a) = 60.5(6) GPa [K0T(a)’ = 6.1(2)]; K0T(b) = 122.8(2.6) GPa [K0T(b)’ = 5.7(8)]; K0T(c) = 119.7(1.5) GPa [K0T(c)’ = 5.1(5)]. Gedrite has a much higher bulk modulus than anthophyllite (66 GPa) and proto-amphibole (64 GPa). All of the three axial moduli of gedrite are higher than those of these two other ortho- amphiboles.
    [Show full text]
  • KYANITE-GARNET GEDRITITE NEAR OROFINO, IDAHO* ANNI Hrbranrn, U
    THE AMERICAN MINERAIOGIST, VOL. 44, MAY_JUNE, 1959 KYANITE-GARNET GEDRITITE NEAR OROFINO, IDAHO* ANNI HrBraNrN, U. S. GeologicalSuraey, Menlo Park, Californio. ABSTRACT In Clearwater County, Idaho, kyanite is found with amphibole in two rock types, (1) in kyanite-garnet gedritite near Orofino and (2) in hornblende-bearing iayers of anorthosite in the Boehls Butte quadrangle. The associated rocks near Orofilo are garnetiferous biotite gneisses,hornblende-biotite gneiss, garnet amphibolites, quartzites, and lime-silicate rocks of sedimentary origin. The major constituents in the kvanite-garnet gedritite are gedrite (38 per cent), quartz (26 per cent), oligoclase (16 per cent), and garnet (14 per cent). One to two per cent of kyanite in light bluish crystals is scattered throughout the rock. The formula of the gedrite calculated from the chemical analysis is (K6 s1Na6eoCao ooMg:.soFe 1.57Mn 6.6aTi" e.e7Pe.61Feo olAlno)>:z ca (Sie.nA1r.or)>-r. oo(On.ro(OH)r.s0) >:2a. 00. The garnet consists of about 49 per cent almandite and 43 per cent pyrope with some spessartite, grossularite, and andradite The texture suggests that gedrite and garnet crystallized later than the other minerals. The chemical analysis of the gedritite shows more than 15 per cent Al:Or, about 8.5 per cent each of FeO and MgO, but only 0.2 per cent K2O and 1.7 per cent CaO. The hornblende- and kyanite-bearing layers of the anorthosite are described briefly for comparison. The kyanite in these layers is a relict mineral, inherited from the schist that formerly occupied the area now covered by anorthosite.
    [Show full text]
  • Protolith Composition of Cordierite–Gedrite Basement Rocks
    607 The Canadian Mineralogist Vol. 45, pp. 607-629 (2007) DOI : 10.2113/gscanmin.45.3.607 PROTOLITH COMPOSITION OF CORDIERITE–GEDRITE BASEMENT ROCKS AND GARNET AMPHIBOLITE OF THE BEARPAW LAKE AREA OF THE THOR–ODIN DOME, MONASHEE COMPLEX, BRITISH COLUMBIA, CANADA Alana M. HINCHEY§ and Sharon D. CARR¶ Ottawa–Carleton Geoscience Center, Department of Earth Sciences, Carleton University, Ottawa, Ontario K1S 5B6, Canada Abstract The Thor–Odin dome of the Monashee complex, southeastern Canadian Cordillera, British Columbia, contains basement gneiss of North American tectonic affi nity, including a distinctive cordierite–gedrite rock that is restricted in occurrence to the basement rocks and a regionally occurring garnet amphibolite. All of these rocks were penetratively deformed and meta- morphosed at upper-amphibolite to lower-granulite facies conditions in the Cordilleran orogeny during the Late Cretaceous to Paleocene. The cordierite–orthoamphibole (dominantly gedrite) unit appears to defi ne a discontinuous marker horizon or horizons within the Paleoproterozoic basement paragneiss. The cordierite–gedrite rocks have a unique bulk-rock composition that is char- acterized by depletions in the alkali elements and Ca, and enrichments in Al, Mg and Fe. They have fl at rare-earth element (REE) patterns, depletions in most low fi eld-strength elements (LFSE), and enrichments in high fi eld-strength elements (HFSE). The 87 86 measured Sr/ Sr values for these rocks vary from 0.74923 to 0.85962, and the ␧Nd(today) values vary from –15.3 to –20.6. The cordierite–gedrite rocks are interpreted as Paleoproterozoic mafi c volcanic rocks that were hydrothermally altered, likely prior to metamorphism.
    [Show full text]
  • Red Corundum, Sapphirine and Kornerupine from Kittilä, Finnish Lapland
    RED CORUNDUM, SAPPHIRINE AND KORNERUPINE FROM KITTILÄ, FINNISH LAPLAND ILMARI HAAPALA, JAAKKO SIIVOLA, PENTTI OJANPERÄ and VEIJO YLETYINEN HAAPALA, I., SIIVOLA, J., OJANPERÄ, P. and YLETYINEN, V.: Red corundum, sapphirine and kornerupine from Kittilä, Finnish Lapland. Bull. Geol. Soc. Finland, 43, 221—231. Mineral assemblages containing corundum, sapphirine and kornerupine are present in a high-grade metamorphic amphibolite-hornblendite formation near the great granulite complex of Finnish Lapland. A low-grade metamorphism has slightly retrogressed the mineral assemblages and partly destroyed corun- dum, sapphirine and kornerupine. Chemical analyses and physical properties including single-crystal data are presented for hornblende, gedrite, sapphirine and kornerupine. Ilmari Haapala, Jaakko Siivola, Pentti Ojanperä and Veijo Yletyinen, Geological Survey of Finland, Otaniemi, Finland. Introduction conrundun (ruby), panning was carried out on the spot. A great deal of corundum was obtained In September, 1965 the Geological Survey of by panning the soft rock weathered during pre- Finland received a small boulder containing red glacial time and now located beneath the normal corundum (Fig. 1) from a place called Paaraskalla moraine. Many of the corundum crystals were in the Kittilä wilderness in Finnish Lapland. This weakly translucent and of a pink or red colour, sample was found by a school-boy, Mikko Tervo. but no precious corundum was found. Six During short periods in 1966—68 the area was crystals were polished by Mr. Tauno Paronen, studied for economic corundum deposits, and but no star figures were visible. The amount of many tens of boulders and some outcrops con- corundum in the rock is so small and the crystals taining corundum were found.
    [Show full text]
  • Cummingtonite (Mg; Fe )2(Mg; Fe )5Si8o22(OH)2 C 2001 Mineral Data Publishing, Version 1.2 ° Crystal Data: Monoclinic
    2+ 2+ Cummingtonite (Mg; Fe )2(Mg; Fe )5Si8O22(OH)2 c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Monoclinic. Point Group: 2=m: As bladed, columnar, or ¯brous crystals and ¯brous aggregates, to 20 cm. Twinning: Simple or multiple twinning 100 . k f g Physical Properties: Cleavage: Good on 110 , intersecting at 54± and 126±. Tenacity: Brittle. Hardness = 5{6 D(meas.)f= 3.g1{3.6 D(calc.) = 3.3 Optical Properties: Transparent to translucent. Color: Dark green, brown, gray, beige; colorless to pale green in thin section. Luster: Vitreous. Optical Class: Biaxial (+). Pleochroism: With increasing Fe content, weak; X = Y = colorless; Z = pale green. Orientation: Y = b; Z c = 21± to 16±; X a = 9± to ^ ¡ ¡ ^ ¡ 3±. Dispersion: r < v; weak. ® = 1.632{1.663 ¯ = 1.638{1.677 ° = 1.655{1.697 ¡ 2V(meas.) = 70±{90± Cell Data: Space Group: C2=m: a = 9.516(5) b = 18.139(10) c = 5.311 ¯ = 102:1± Z = 2 X-ray Powder Pattern: Labrador City, Canada. 8.30 (100b), 3.06 (90), 3.26 (80), 2.754 (70), 1.403 (60), 9.12 (50), 2.623 (50) Chemistry: (1) (2) (1) (2) (1) (2) SiO2 51.53 53.84 FeO 16.91 25.63 Na2O 0.65 0.15 TiO2 0.31 0.01 MnO 0.22 0.19 K2O 0.00 + Al2O3 5.02 1.61 MgO 20.84 17.44 H2O 2.15 Fe2O3 0.82 CaO 1.34 0.41 H2O¡ 0.64 Total 100.43 99.28 2+ 3+ (1) Geodh Dubh, Scotland; corresponds to (Mg4:44Fe2:02Al0:21Ca0:20Na0:18Fe0:09 Ti0:03Mn0:03)§=7:20(Si7:36Al0:64)§=8:00O22(OH)2:05: (2) Orfordville Formation, Mt.
    [Show full text]
  • Orthoamphibole There Are Two Common Forms of Orthoamphibole: Anthophyllite: (Mg,Fe)2(Mg,Fe)5Sio22(OH)2 Gedrite: (Mg,Fe)2(Mg,Fe)3
    Orthoamphibole There are two common forms of orthoamphibole: Anthophyllite: (Mg,Fe)2(Mg,Fe)5SiO22(OH)2 Gedrite: (Mg,Fe)2(Mg,Fe)3Al2[Al2Si6O 22 (OH)2] At high temperatures the two form a continuous solid solution The general formula for amphibole: W 0-1X 2Y 5Z 8O 22(OH)2 For orthoamphible: W X Y Z 8O 22(OH)2 - (Mg,Fe)2 (Mg,Fe)5 Si 8O 22(OH)2 - (Mg,Fe)2 (Mg,Fe)3Al2 Al2Si 6O 22(OH) 2 The W cation fills a ~10-fold coordination site in the amphiboles. It Contains large cations like Na+. In anthophyllite this site is vacant. However, in Gedrite it may sometimes contain Na+ . Physical Properties Color: brown note: the brown color of orthoamphibole may be useful in distinguishing it from hornblende, which usually has a greenish- black color H: 5.5-6 G=2.85-3.57 Cleavage: perfect {210} cleavage like all amphiboles. Also distinct Cleavage on {100} and {010}. Luster: vitreous 1 Optical Properties a =1.587-1.694 b =1.602-1.710 g =1.613-1.722 d =0.013-0.028 Conclusion: moderate to high relief and second and third-order Colors under polarized light. Pleochroism: weak; usually with Z>Y>X Since orthoamphibole is orthorhombic, it is a biaxial mineral with 2Vx anthophyllite= 65-122 o 2Vx gedrite= 72-133o Both minerals may either be optically positive or negative. Either Addition or subtraction may happen to the slow ray of the plane. Ways to tell gedrite and anthophyllite apart: gedrite has a slightly higher index of refraction and is more likely to have a negative optic sign than anthophyllite Crystallography: Orthorhombic Point group: 2/m 2/m 2/m Space group: Pnma 2 .
    [Show full text]
  • Field Relations and Chemistry of Sapphirine
    Canadian Mineralogist Yol. 22, pp. 417421 (1984) FIELDRELATIONS AND CHEMISTRYOF SAPPHIRINE.BEARING ROCKSFROM THE R'@RNESUNDAREA. FISKENESSET,WESTERN GREENLAND HOWARD R. WILLIAMS Dewrtnent of Geologicol Sciences,Brock University, St. Catharines, Ontario L2S 3Al ABSTRACT (1910),has sincebeen found worldwide in hig[-grade met?morphic rocks of diverse composition and his- Two contrasting sapphirine-bearing assemblagesare tory (Hiegins et al. 1979).This paper dessribestlree described: a higbly maguesianone, developed sporadical- more sapphirine-bearing localities some 50 kn east ly at the upper contact of the FisketrEssetComplex in as- of the tlpe locality. Herd et al. (1969) and Herd sociation with layeredultramafic rocks, and the other, more (1973) reinvestigated the Fiskenaessetlocality, iron-rich, in the amphibolite bordering the Complex. Miner- describing it in detail; the sapphirine was found to al assemblagesdescribed (1) are oftwo kincls: iron-poor: be associatedwitl rocks marginal to the Fiskenas- enstatite - phlogopite - olivine - pargasite - - sapphirine (Windley spinel, gedrite - sapphirine - spinel, and enstatite - gedrite set Complex et al. 1973). - phlogopite - sapphirine - spi4el; (2) iron-rich: magnesio- The tlree occurrencesdescribed in this paper have hornblende - sapphirine - spinel - anorthite. Only the iron- similar field relations to the classicFiskenasset lo- poor sapphirine-bearing assemblagesand their associates cality Gig. l). The local geologyis dominatedby a are characterizedby the presenceof accessoryapatite, ru- high-eradequartzofeldspathic gneiss terrane contain- tile and zircon, which may indicate a possible sedimentary ing intercalated layers of amphibolite and outlying origin for at least some of the sapphirine-bearing materi- parts of the Fiskenessetgemplex. Petrographic evi- al. The iron-rich assemblageis found within rocks consi- dence indicates that these rocks failed to enter dered to be entirely of igneous origin.
    [Show full text]
  • Properties of Common Minerals Groups Considered Framework Silicates Feldspars Feldspar Twinning K-Spars
    Groups Considered Properties of Common • Framework silicates Minerals • Sheet silicates • Pyroxenes Figures from Winter’s web page (2002) • Amphiboles • Other Silicates • Non Silicates Framework Silicates Feldspars • Simple chemistry •Feldspars • Substitution of Na for K or NaAl for CaAl • Feldspathoids • Crystal systems • Silica polymorphs – Monoclinic (orthoclase, sanidine) – Triclinic (plagioclase, microcline) • Tabular habit Feldspar Twinning K-spars • Simple twins (two parts) • Orthoclase, Sanidine, Microcline – Carlsbad • All optically negative – Common in monoclinic feldspars • All have n ~ 1.53 • Polysynthetic twins • Distinguished by 2V – Albite and others – Sanidine 2V = 0-30º – Common in triclinic feldspars – Orthoclase 2V = 30-70º – Microcline 2V = 70-90º • Microcline has Scotch plaid twins 1 Plagioclase Common Sheet Silicates • Refractive index increases with Ca content •Muscovite – Varies between 1.53 (Ab) to 1.57 (An) • Phlogopite • 2V is large and varies with composition • Biotite • Optic sign depends on composition (+/-) • Chlorite Sheet Structures Phyllosilicates Classified on the basis of Si-O polymerism SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5] Apical O’s are unpolymerized and are bonded to other constituents 2- [Si2O5] Sheets of tetrahedra micas talc clay minerals serpentine Building Blocks Common Sheet Properties • Tetrahedral layers • Crystals are platy parallel to (001) • Perfect cleavage follows (001) • Octahedral layers • 2V is small (0-40º) • Large Cation layers • Extinction is parallel to (001) •
    [Show full text]
  • Field Relations and Chemistry Of
    Canadian Mineralogist Yol. 22, pp. 417421 (1984) FIELDRELATIONS AND CHEMISTRYOF SAPPHIRINE.BEARING ROCKSFROM THE R'@RNESUNDAREA. FISKENESSET,WESTERN GREENLAND HOWARD R. WILLIAMS Dewrtnent of Geologicol Sciences,Brock University, St. Catharines, Ontario L2S 3Al ABSTRACT (1910),has sincebeen found worldwide in hig[-grade met?morphic rocks of diverse composition and his- Two contrasting sapphirine-bearing assemblagesare tory (Hiegins et al. 1979).This paper dessribestlree described: a higbly maguesianone, developed sporadical- more sapphirine-bearing localities some 50 kn east ly at the upper contact of the FisketrEssetComplex in as- of the tlpe locality. Herd et al. (1969) and Herd sociation with layeredultramafic rocks, and the other, more (1973) reinvestigated the Fiskenaessetlocality, iron-rich, in the amphibolite bordering the Complex. Miner- describing it in detail; the sapphirine was found to al assemblagesdescribed (1) are oftwo kincls: iron-poor: be associatedwitl rocks marginal to the Fiskenas- enstatite - phlogopite - olivine - pargasite - - sapphirine (Windley spinel, gedrite - sapphirine - spinel, and enstatite - gedrite set Complex et al. 1973). - phlogopite - sapphirine - spi4el; (2) iron-rich: magnesio- The tlree occurrencesdescribed in this paper have hornblende - sapphirine - spinel - anorthite. Only the iron- similar field relations to the classicFiskenasset lo- poor sapphirine-bearing assemblagesand their associates cality Gig. l). The local geologyis dominatedby a are characterizedby the presenceof accessoryapatite, ru- high-eradequartzofeldspathic gneiss terrane contain- tile and zircon, which may indicate a possible sedimentary ing intercalated layers of amphibolite and outlying origin for at least some of the sapphirine-bearing materi- parts of the Fiskenessetgemplex. Petrographic evi- al. The iron-rich assemblageis found within rocks consi- dence indicates that these rocks failed to enter dered to be entirely of igneous origin.
    [Show full text]