MINERALOGICAL NOTES 913 Cooling Histories of the Pyrrhotites

MINERALOGICALNOTES 913 cooling historiesof the pyrrhotites, becauseslow cooling would tend to favor the formation of monoclinic pyrrhotite, particulariy for pyrrho- tites with compositionsnear the upper limit for iron. For lesseramounts of iron it would probably appearas a distinct phaseregardless of cooling history. It is hopedto verify this relationshipby heatingand slowcooling of natural pyrrhotites acrossthe transformation boundary between the hexagonaland monoclinicphase.

RBrnntmcos

AnNor-n, R. G. (1962) Equilibrium relations betrueenpyrrhotite and pyrite from 325o to 743" C. Econ. Ge01.57,72-91. --- ANDL. E. RnrcsrN (1962) Measurement of the metal content of naturally occur- ring, metal-deficient, hexagonal pyrrhotite by an r-ray spacing method ' Am Mineral' 47,105-111. Bvstnon, A. (1945) Monoclinic magnetic pyrites. Arkh. Kemi. Mineral' Geol' l9B (8), 1-8' GndNvor.o, F. aNl H. HanalnsnN (1952) On the phase relations of synthetic and natural pyrrhotites (Fer ,S) Acta ChemicoScand.6,1452-1469.

THE AMERICAN MINERALOGIST, VOL. 48, JULY-AUGUST' 196.3

THE UNIT CELL AND SPACEGROUP OF STEWARTITEI Dor.raro R. Pnacon, Departmen'tof Geologyand, Mineralogy, The (Iniversity of Michigan, Ann Arbor, Mi,chigan'

Tennyson(1956) reported. that stewartite,MnFez (OH), (PO*)r' 8H20, is monoclinicwith the unit cell parameterslisted in Table 1. The value of the magnitude of b(60.8 A) is exceptionallylarge by comparison with parametersof reducedunit cells of most inorganic substances.Accord- ingly, the unit cell has beenreinvestigated. Crystalsof stewartitefrom the Palermoand Fletcherquarries, N. Gro- ton, N. H., were used in this investigation. The stewartite from the Palermo quarry occursas radiating groupsof small yellow crystals asso- ciatedwith strunzite,Iaueite, eosphorite,"diadochite," rockbridgeite, and siderite, while that from the Fletcher quarry occurs as aggregatesof yellow crystalsin cavitiesin rockbridgeitewith hureaulite,strengite and metastrengite.In both casesthe mineralsare alteration products of tri- phylite. The identity of the stewartitewas confirmedwith powder photo- graphs, the patterns correspondingclosely to those describedby \{ur- doch(1958) and Neves(1958, 1960). The crystals from the Palermo quarry resembiethose describedby Tennyson from Hagendorf, and are bounded by three pinacoids' Rota-

I Contribution No 251 The Mineralogical Laboratory, Department of Geology and Mineralogy, The University of Michigan. 914 MINERALOGICAL NOTES

Taer,n 1. UNrr Crr,r, Dera non Srnw,rnrrrn .q.NoLeurrrn

Stewartite Stewartite Laueite Tennyson this this Strunz (1es6) work work (19s4)

7.r7A 2x5.23A 7.2s4 s.28A b 60.8 r0.77 609 10.66 c 10.41 725 2x5.2s i 1i a 900 90035' 90"52', 107055', B 109032, 109058', 109058', 110'59', ^l 900 7l"2l' 88.01', 71"07, Symmetry or monoclinic PI or Pl 1or1 Pl or Pl space group Z 72 2 t2 1

tion and weissenbergphotographs obtained with eachof three principai zone axesas rotation axesshowed that stewartite is triclinic with space group P1 or P1. Unit cellparameters are tabulatedin Table 1.There is an obviouscorrespondence of the magnitudesof a, c andB to the elements,, a and B, respectively,of the unit cell determinedby Tennyson.A six-fold primitive unit cell with pseudomonoclinicgeometry may be chosensuch that

b,:-2a + 61-; i' : i,. The dimensionsof this cell are listed in the third column of rable 1. There is a closerelationship between this celland that determinedby Tennyson. The unit cell of stewartite is closelyreiated to that of the polymorph laueite. The parameters of the laueite unit cell were determined by Strunz (1954)and are given in Table 1. Rotation photographsof stewart- ite with the o axis as rotation axis show that there is a substructurewith period a/2. The parametersof the subcellcorrespond closely to those of laueite with the exceptionof the value of the angleo. RnlrnrNcns Munooctt, Josnrn (1958) Phosphate minerals of the Borborema pegmatites: rI- Boqueirlo. Am. Mineral. 43, 1148-1156. Nrvns, J. M. connpre (1958) Novos minerais dos pegmatitos do Mangualde (portugal) Mem. e Not., Mus. Lab. Mi.n. GeoI., (Jnia. Coimbra, 46, 56-67. --- (1960) Pegmatitos com berilo, columbite-tantalite e fosfatos da Bendada. Mem. e Not., Mus. Iab Min. Geol , Llnh. Coimbra, SO, l-172. StnuNz, H. (1954) Laueite, MnFez... loH/po4]r.8H2o, ein neues Mineral. Naturwissen. 41,256. TnNwvsoN, Cu. (1956) Das Stewartit-p r oblem. N atur wis sen. 43, 128-129.