389-392 (1981) ... energy-dispersion analysis, appeared to be iso- ... vein selvages, sharing a localized phosphate-rich assemblage comprised largely of. 389 ...
CanadianMineralogist !ol. 19, pp. 389-392(1981) PANASQUEIRAITE, A NEW MINERAL: THE OH.EQUIVALENT OF ISOKITE" ANDREW M. ISAACST AND DONALD R. PEACOR Departmerttof GeologicalSciences,The Universityol Michigan, Ann Arbor, Michigan 48109, U.S.A.
ABsrRAcr Panasqueiraite is a new mineral that occurs as a massive, fine grained pink mineral in specimens from the hydrothermal vein system at Panasqueira. Portugal. It is similar to thadeuite in association and paragenesis. Panasqueiraite is the hvdroxvl analogue of isokite and has the ideal formula CaMgPOr(OH,F). It is opticallv biaxial. positive. a 1 . 5 9 0 ( 2 ) ,P r . s 9 6 ( 2 ) , t 1 . 6 1 6 ( 2 ) , 2 v 5 l ( 2 \ ' , b - Z, Xlrc -122". Panasqueiraitejs monoclinic, a 6.535(3), b 8.753(4). c 6.9re(4) L, P rr2.33?)". V 366.1(6) A', with space group Cc or C2/c, Z - 4. The strongest five lines in the X-rav Dowderdiffraction pattern td in A (I) (ftkl)l are 3.20(67) (002). 3.02(s6)(200), 2.783(3DCIOz)" 2.626 (100)(130), 1]22G3) 2.s84(45)('31,022), (242.222). 1.658(30)(330). The densitv of panasqueiraite is 3.22 e cm-3 (calc.) and 3.27(1) g cm-3 (obs.). Isokite and panasgueiraite are isostructural on the basis of similar chemistries and powder patterns. In the literature, the isokite cell has been described as body-centred instead of C-centred as required by the systematic pxtinctions we observed.
3 . 2 0 ( 6 7 ) ( 0 0 2 ) ,3 . 0 2 ( 8 6 ) ( 2 0 0 ) ;2- . 7 8 3 ( . 3 1 ) ( 2 0 2 ) ' (45\ (l31,02D. r.722(33) ( 130). 2.584 2.626(rOO) de la panasLa densit6 Q42,222'),1.653(30)(330). queiraiteestde 3.22 (calc.), 3.27(l') (obs.).Isokite et panasqueiraitesont isostructurales.autant que puissentl'indiquer un m6me chimismeet des clich6s de poudre semblables.Les travaux ant6rieursont attribu6 ir la maille de l'isokite le mode "maille centr6e" plut6t que "maille b face C centr6e" qu'indiquent les extinctions syst6matiquesobserv6es. (Traduit Par la R6daction) Mots-clds:isokite,espEcemin6ralenouvelle.Panasthad6uite. queira (Portugal), panasqueiraite. INrnooucrtou
During the course of an electron-microprobe study of a suite of fluorine- and hydroxyl-bear' ing phosphate-rich specimens from the hydrothermal vein system at Panasqueira, Portugal, we encounteredmaterial that, on the basis of an energy-dispersionanalysis, appeared to be isoKeywo:'ds: isokite. new mineral description. Panaskite (CaMgPOeF). Upon obtaining quantitative oueira, Portugal. panasqueiraite.thadeuite, wavelength-dispersionanalyses, we found that, as for several associated phosphates' this maSoruvltnB terial is enriched in the hydroxyl ion and is the panasqueiraile, se hydroxyl analogue of isokite. We have named nouvelle espEce min6rale. La prdsente sous forme massive: elle est rose. finethis new mineral panasqueiraite after the type ment grenue dans des 6chantillons recueillis dans locality. The mineral and the name have been le systbme de filons hydrothermaux de Panasqueira approved by the I.M.A. Commission on New (Portugal). Elle ressemble b la thad6uite Dar ses Iriinerals and Mineral Names. Type material is min6raux associ6s et sa paragen6se. De formule present in the collections of the Department -of id6ale CaMgPO,(OH,F). elle est l'analogue hvdrobeological Sciences, the University of Michip positive. 1.590Q), Biaxe l'isokite. xvl6 de d gan and the Smithsonian Institution (N.M.N.H. 2Y 5r(2\', b z, XN 1.596(2), t r.616(2), - +22o. La panasqueiraiteest monoclinique,a 1M521). 6.535(3), 6 8.753(4), c 6.919(4't A. P The general geological setting of the Panasll2.33(4')o, v 366.1(q As, groupe spatial Cc queira tin-tungsten deposits is described by ou C2/c, Z - 4. Les cinq raiesles plus intenses Thadeu (1951) and Conde et al. (1971), and sont the general mineralogy of the veins ir sumdu ctich6 de poudre ld en A(t)fhtl)t marted by d'Orey (1967), Gaines & Thadett 'lContribution No. 371 from the Mineralogical (1971) and Kelly & Rye (1979). The associaLaboratory, Department of Geological Sciences, tion and paragenesis of panasqueiraite are The University of Michigan, Ann Arbor, Michigan. identical with those of thadeuite (Isaacs er a/. 1979). Both panasqueiraite and thadeuite are fPresent address: Planetary and Earth Sciences in the vein selvages,sharing a localized found Division, C-23, NASA/JSC, Houston, Tx 77O58, phosphate-rich assemblagecomprised largely of u.s.A. 389
390
THE CANADIAN MINERALOCIST
fluorapatite,wolfeite, topaz, muscovite,sphaler- a solution of methyleneiodide and acetone;the ite, quartz' chalcopyrite,. pyrrhotite, siderite, ;.rJt-;l ,i"'-"i"ni"g liquid was determined arsenopyrite, minor chlorite and rare vivianite by pycnometer. and althausite. CnysrellocnApHy AND Srnucrunr
PHysrcel pRopERTrEs
Cell dimensions and symmetry were deterPanasqueiraite occurs as a massive. fine mined using precessionsingle-crystal X-ray-difgrained pink mineral in aggregatescommonly fraction techniques on two individual crvstals. several centimetres in diameter. No crystil Panasqueiraiteis monoclinic; extinctions are faces are observedin any of our material, lihich consistent with two space groups, Cc and C2/c. consistsof-randomly intergrown grains typically Unit-cell parameterso obtained by least-squares about a millimetre in size. panasqueiraii" t u. u refinement of 25 uniquely indexed powder-difpoor {010} cleavage, vitreous lustre. white fraction data, are a 6.535(3), b 8.753(4), c streak and a Mohs hardness of 5. Although 6.919(4) A, B tt2.33(4)o. powder-diffraction it does not fluoresce under ultraviolet radiation, data for panasqueiraite are presented in Table it does exhibit a blue cathodoluminescence in I along with selected powder-diffraction data an electron beam at a 12 kV potential. It is for isokite. lp]ically biaxial, positive, nonpleochroic, d. It is likely that panasqueiraiteand isokite 1 . s 9 0 ( 2l )l ,t . s e 6 ( z y) , 1 . 6 1 6 ( i ) , 2 sv t ( z ) " (obs.), b - Z. X;c 12i". The densityof panas_ are isostructural, on the basis of their similar chemistries and the similarity of the diffraction queiraite is 3.22 g cm-, (calc.) and 3.27(l) data for the two minerals, given in Table 1. g cm-t (obs.), as determinedby suspensionin The cell dimensionsreported for isokite, howTABLEI. POI,IDER.DIFFRACTION DATAFORPANASQUEIMITE ANDSELECTED POI'|DER-DIFFRACTION DATAFORISOKITE
d1obr.;pun.1t/ro
4 .3 6 3.61 3.43 3.20
d(calc.) hkl
q
o20 021
d1obr.;iro.**
67
4.38 3.61 3,44 3.20
o02
3 . 18 5
3.02
86
3.02
200
J.VZs
2.783 2.626 2.5U
?1
2.789 2.628 l.2. s85 L2 . 5 8 3
202 130 l3T o22
2.229 2.220 2.106 2.072 2.041 I
?
100
4s
18 l8 20f 14 l6
1.873 'I .821 1.808 1.771
I
z ..071
113 1f 3]l221
4.38 3,62
2.487
t.c+J
2. 301 2.222 2.105
6 7
.871
202
1,872
2
| .6J/
1.819
313
11.806 1.772
042 240
fr.8oe r33
14
dlcaic.) hkr
d(obr.)r.0.
r | .722 242
1 .740 | .720
L 1. 7 2 0 I I .708 L I.706
222
ztu' 332
t./u5
I .684 1 .671 1.658 I .599
.045 .964 .948 .884
9 7
1.706
2.87 2.7U 2.630 2.586
2,069 2.041 1 ,962 1.946 'I .886
L,
1.722
J. +f,
041 312 310 223 132
OA?
t .948 I .880
229 2 .2 r 8 a . r 09 L z . ]06 Z.
lIl
d 1 o b r . ; p u n u .t l t o
1 qqo
9 30 2
t.go
JJU
004 1Q 24i
t.f,5d
o
| .54J
L 1 .496
qD 400 203 33'l
1. 4 7 9
'r34
1.5?4
t.aa5
r .430 | ,426 1.394
| .05d
I .600
IJ
'I
1.5i2 I .496 I .481
1.670
a
il 6 20
7
'r5T
Et1
r r .496
1 ,429 1.4?8
r'r
?oR
Li :;,;
420 152 4M-
I .671 i.656 1.602 L539 1. 5 2 2 I.510 1 .495 1 .479 I .453 1.428 1 .392
| 5J
I r.346 244 I r.346 3fl I r .345 ll5
I .388 1.344 'I .313 I .303
and quartz as an internal standard. Cilculatedd-va1uescoi""spon4-to-pinasquetratte observedvalues. **IsokJte data are thoseof Deans & McConnet.l frSSsi wilh-l ;-i:i i.
PANASQUEIRAITE. THE OI{.EQUIVALENT OF ISOKITE
391
(Deans & McConnell 1955). The higher spaceever, are a 6.52, b 8.75, c 7.9I A, B tZt.+Z' (Deans & McConnell 1955), quite different group symmetry is apparently dependentPrin'F from those of panasqueiraite. trn the original cipally on the substitution of the'smaller descriptionof isokite, Deans & McConnell sup- ion for As in the tetrahedral site in tilasite. On plied 60 powder lines with relative intensities, this basis we infer that the panasqueiraitestrucbut did not index the data. In examining their ture probably has space grotrp A/c. tabulation, we found that none of the major powder lines given could be indexed using the CHrvrstnv lattice parameters that they had determined. Electron-microprobe analyses(Table 2) were However, we found that by using the panasqueiraite lattice parameters, we were able to carried out using an ARL-EMX instrument index all of the powder lines for isokite with with three wavelength-dispersionspectrometers intensities reported as 'omoderate" or stronger, using LiF, PET and TAP crystals. Standards used were apatite for Ca, P and F. clinopyas well as the d values that we determined for panasqueiraite.Using the C-centring axial trans- roxene for Fe and Mg, and synthetic tephroite formation (100/010/T0T) on a body-centred for Mn. The analyseswere made with a 0.015 isokite cell, we obtained the parametersa 6.52, plA specimen current and 12 kV excitation h 8.75,c 7.16 A, /J 109.50',which are approxi- potential; drift, atomic number, fluorescence Deans and absorption corrections were applied to the mately those reported for panasqueiraite. & McConnell (1955) have therefore reported raw data using the program EMPADR VII the space group C2/ c for isokite and apparently (Rucklidge & Gasparrini 1969). have given the unit-cell dimensionsbasedon an The cell contents were calculated using the I-centred cell. The ability to index isokite using results of the chemical analysis, measured denthe panasqueiraitecell dimensionsis consistent sity and refined cell parameters. The results with the isostructural nature of the two minerals. indicated that there are four P per unit cell, The following discussionof structuresis based consistent with the isokite structure; we thereon this premise. fore normalized the atomic ratios to four P Povarennykh (1972) describedisokite as iso- atoms (Table 2). The ideal formula of panasstructural with titanite, i.e., it is a structure queiraite, with Z = 4, is CaMgPOo(Oq'F), 9H dominated by chains of vertex-sharingMgOu > F, with trace amounts of iron substituting octahedra parallel to a. The chains are crosslinked by POe groups" resulting (by analogy with the description of the titanite structure of ANALYSIS Speer & Gibbs 1976) in a (MgOPO,) frame- TABLE2. ELECTRON-MICROPROBE OFPANASQUEIRAITE work with large cavities enclosing the sevenfold-coordinatedCa. Fluorine occupiesthe same site in isokite as does the nontetrahedral oxygen Atons/CelI lIJt.% in titanite. In reporting their refinement of the strtlcture of tilasite, Bladh er al. ,1972) noted that this 3.95 3'l.0 Ca0 mineral, which is the As-analogue of isokite 0 .00 0 . 0 Mn0 is slightly and is also isostructural with titanite, 0.04 0.4 Fe0 noncentric. with spacegroup Cc. The explana4.06 22.9 Mgo tion supplied for this is that the F and Ca sites 3.98 3 9. 6 Pzos are displaced from the pseudo-2r axis in space grotrp Cc,' the latter displacement was deter1. ' t 7 3.1 F mined nnambiguously. The resulting structural 2.82 6 . 7 0 H * distortion, combined lt/ith a slight rotation of the arsenategroup, requires the lowering of the I 03.7 symmetry of the cell. The tilasite, isokite and panasqueiraitestrucLess0 tures all have at least Cc symmetry. The strucf o r F , 0 H--395 : 4.4 ture of tilasite has been shown to be of no higher symmetry, but the isokite strllcture has bein postulated to have a C2/ c cell on the basis * 0 H c a l c u l a t e da s s u m i nPg: ( 0 H + F=) l : 1 . of a negative result in a test for pyroelectricity
392
THE CANADIAN MINERALOGIST
for magnesium on the octahedral site. No Cl was observed in any of the energy-dispersion spectra obtained. - Whereas all the specimensof panasqueiraite from the Panasqueira vein system studied here were found to have OH > F, samples from other areas of the district have F ) OH and are therefore isokite. In none of our material did the two phasescoexist; however, it appears that the presence of one or the other mineral is a function of the local activities of OH- and F- in the vein-forming solutions. Associated wolfeite, also with OH > F, was found to contain ( O.lVo Ca by weight and a Fe:Mn ratio of 1:2. No As was detectedin any of the phosphates in this assemblage. ACKNoWLEDGEM ENTS
DEeNs, T. & McCoNNerr, J.D.C. (1955): Isokite, CaMgPOrF, a new mineral from northern Rhodesia. Mineral. Mag. 30, 681-690. n'Onsy, F.C. (1967): Tungsren-tin mineralization and paragenesis in the Panasqueira and Vale da Ermida mining districts, Portugal. Serv. Geol. Port. Comun. 52, 117-168. CArNEs,R.V. & Tneoru, D. (1971): The minerals of Panasqueira,Portugal. Mineral, Rec, 2,73-78. Iseecs, A., PEAcoR,D.R. & Kerrv, W.C. (1979): Thadeuite, Mg(Ca,Mn) (Mg,Fe,Mn)r(PO4)r(OH, F)r, a new mineral from Panasqueira,Portugal. Aner. Minetal. 64. 359-361. KELLv, W.C. & Rvr, R.O. (1979): Geologic, fluid inclusion, and stable isotope studies of the tintungsten deposits of Panasqueira, Portugal. .Ecaa. Geol. 74, 1721-1822. PovenrNNyxn, A.S. (1972): Crystal Chemical CIas-
sificution ol Minerals 2. Plenum Press.New York. We are grateful to Dr. J.A. Mandarino for RucrLrocr, J.C. & GasrennrNl, E. ( 1969): his careful review of and valuable suggestions EMPADR VII. Specilications ol a Computer regarding this manuscript. REFERENCES Bleos, K.W., CoRBErr, R.K., McLseN, W.J. & LaucnoN, R.B. (1972): The crystal structure of tilasite. Amer. Mineral. 5?, lgti0-lgS4. CoNoE, L,N., PrnErne, V., Rrnrmo, A. & Tneosu, D. (1971): lazidas Hipoginicos de Estanho e Volfrdmio. Guidebook, excursion ?, Congresso Hispano-Luso-Americano de Geol. Econ., iirec_ gio-General Minas Serv. Geol., Lisboa, portugal.
Program lor Processing Electron Microprobe Analytical Data. Dep. Geol. Univ. Toronto.
Spmn, J.A. & Grssq G.V. (1926): The crystal structure of synthetic titanite, CaTiOSiOa and the domain texture of natural titanites. Amer. Mineral. 61. 238-247. Tseoru, D. (1951): Geologia do couto mineiro de Panasqueira.Serv. Geol. Port. Comun. 92. 5-64. Received February '/98./, revised manuscript accepted April 1981.
