STUDIES IN THE MICA GROUP; SINGLE CRYSTAL DATA ON PHLOGOPITES, BIOTITES AND MANGANOPHYLLITES A. A. LBvTNSoNAND E. Wu. Horwucu, Department oJ Mineralogy, The Ohio State [Inioersity, Columbus, Ohio, and. Department of Minerology, Uni.aersityoJ Michigan, Ann Arbor, Michigon. AssrnA.ct Weissenberg studies of about 250 specimens of phlogopite, biotite and manganophyllite, of which 63 have been chemically analyzed, indicate: (1) in phlogopites there is no dis- cernible relationship between structure and either composition or paragenesis; (2) in biotites there is no relationship between structure and composition, but geologic environ- ment may be a factor in determining the polymorphic type; (3) the optic plane of all 2-layer polymorphs is normal to (010), as is also the case for the biotite variety, anomitel and (4) lJayer polymorphs nearly always have the optic plane parallel with (010), which corresponds with the orientation of the biotite variety, meroxene. IxrnooucuoN Systematic variations between composition and the various poly- morphs in the muscovite-lepidolite series have been demonstrated by Levinson (1953). On the basis of these results it seemeddesirable to investigate the biotite-phlogopite seriesin a similar manner in the hope of gaining insight into causes of the complex polymorphism known to exist in these micas. The only other Weissenbergstudy of these micas known to the writers is in the work of Hendricks and Jefferson (1939), predominantly on unanalyzed specimens. We have obtained over 60 analyzed specimensof biotite, phlogopite and manganophyllite (which we consider as manganoan phlogopite), most of which have been describedby several investigators. In addition we have studied a suite of approximately 200 unanalyzed biotites and phlogopites from geologically well-studied occurrences. AII specimens were studied by meansof the Weissenbergmethod using copper radiation. In most casesonly zero level, o-axis photographs were taken, as these are sufficient to determine the Iayer periodicity. In many cases,however, upper level photographs were taken, which confirmed the structure identification based on the zero level, o-axis photographs. In agreement with Hendricks and Jefierson (1939, p. 762), the 3-layer polymorph is considered to be hexagonal (actually trigonal) as a limiting case, even though some specimensare not truly uniaxial. Orientation of the flakes was securedby optical methods in those casesin which 2V was approxi- mately 10o or greater. Laue photographs and percussion figures were Contribution from The Department of Mineralogy and Petrography, University of Michigan, No. 185. 937 938 A, A. LEVINSON AND E. WM. HEINRICH Tlsr,n 1. Srnucrunrs ol ANAr,yzEDPnr,ocoprrrs Num- Relerence Structure Occurrence FeO FerOr MgO ber TiOr F 1054 Jakob (1938) ? Very difiuse Irom Morawita, 0.64 1.05 26.77 0.10 0 00 scattering Czechoslovakia 1055 Jakob (1931)No.55 1-layer mica peridotite, 2.52 0.OO 25.45 2 80 0.00 t (mod. scat- Italy I 1056 I No.73 lJayer Bugess, Ontarior 1.24 0.73 26 4-s 1.15 1.00 1057 S NoTo 1-layer Rossie, N Y 2 4.79 0.00 22.30 4.O7 012 1058 3 No.6e 1-layer Hull, Quebect 2.49 0.7t 21 60 1.74 2.O4 1059 6 No.68 1-1ayer Burgess, Ontarior 0.30 0 00 27.32 0.39 6.74 1060 E No.oz 1-layer Burgess, Ontariol 1.50 0.00 26.t4 0 86 2.37 1061 3 No.oo lJayer fwlo, Madagascara 3.28 0.00 25 29 2.r9 l. l.r 1062 $ Noos 2-layer Ampandrandara, 2.96 1.18 23.40 1.69 0.68 a (mod. scat- Madagascars 1063 F No.oa 1-layer Mandridano, Mad- 2.09 0.00 24.48 1.64 0.08 1064 t No. o.r 2-layer Saharakara, Mad- 2.79 1.68 23.78 1.tl 0.56 I ag3 1065 I No62 1-layer Anbatoabo, Mad- L.42 0.66 24.80 0.86 0.86 J 1066 Jakob (1928)No. 19 1-layer Simplon Tunnel, 0 00 1.71 24 19 0.39 0.00 (hor1r scat- Switzerland 1067 Jakob (1928)Nc 20 1-layer dolomite-Tessin 0.00 1.31 25.81 0.83 0.00 1068 Jakob (1928)No.22 llayer contact metamor- 2 72 0.97 25.05 0.66 0.5E phic S. W. Africa 1069 Jakob (1928)No.23 1-layer pneumatolytic, Ve- 0.58 1 92 28.18 1.27 suvius, Italy 1071 Jakob-not pub- 1-layer Skr?ibbiile, Pargas, 0.71 1 01 27.80 0.12 2.tl lished Finlanda toI2 Jakob-not pub- 1-layer Pargas, Finlandr 5.59 1.54 22 00 L.41 2.80 lished 1073 Jakob-not pub- 1-layer Patteby, Pargas, t.47 1.29 26.16 0.33 1.87 lished Finlanda 1074 Jakob-not pub- 1-layer Ontala, Pargas,4 1.68 1.8? 25.91 0.68 1 30 iished Finland 1075 Jakob-not pub- 1-layer Skriibbdle, Pargas, 0.59 1.75 27.22 0.10 0.48 lished Finlanda 949 Dana (1892) 1-layer Rossie, N Y.2 7.62 1.12 21.47 1 16 4.00 Anal. 12p 633 1135 Pagliani (1940) 1-layer marble, Italy 1.55 2.65 27.52 2.83 1139 Hutton and llayer rorble, New Zea- 2.38 0.43 22.95 0.82 0.62 Seeyle (1947) land 1252 Pieruccini (1950) 1-layer pneumatolytic, Mt. 7.89 tr. 15.66 0.33 2.57 Sonm, Italy 1-layer\ Ambatoabo, Mad-\ 2 30 n.d. 24.42 O.74 n.d. 1261. [{d <t){") IMauguin (1928) 3-layerl agascar,s I 730 Prider (1939) 1-layer leucite lamproite,s 3 75 2.r8 19.66 8.97 0 66 West Australia 1325 Cross (1897) lJayer in wyomingite,s 0.90 2.73 22,40 2.09 2.46 Leucite Hills, wyo. (1) The Quebecand Ontario phlogopites occur in pegrotitic bodies asrcciated with pyroxenite and narble, (2) The occurrencesnear Rossie, St. Lawrence, N. Y, are in marble. (3) The Madagascar deposits are similar to the Canadian type (4) The oconences at Pargas are in mrble, (5) Of pyrogenic origin. STADIES IN THE MICA GROL.P 939 usedin the majority of the caseslfor the most part the percussionfigure method was found to be unreliable. This study is a part of the researchprogram, ,,Natural Mica Studies," sponsored by the U. S. Army Signal Corps, Squier Signal Laboratory, Ft. Monmouth, New Jersey, under the general supervision of Dr. S. Benedict Levin and administered as Project M-928 of the Engineering ResearchInstitute, University of Michigan (Heinrich, et al., l9S3).The writers are indebted to Dr. Levin for his general assistance,to professor Duncan McConnell for critically reading the manuscript, and to the following for gifts and loan of specimens:prof. C. Frondel, Dr. A. F. Hallimond, Prof. C. O. Hutton, Prof. J. Jakob, Dr. y. Kawano, prof. C. Mauguin, Dr. and Mrs. A. Miyashiro, Prof. G. p. pagliani, prof. R. L. Parker, Prof. R. T. Prider, Prof. R. pieruccini, Dr. F. T. Seeyle,Dr. K. Sugiura, Dr. G. Switzer, Dr. S. van Biljon, prof. H. Winchell and Dr. H. Yamada. X-ney SruotBs on pnroooprrr The structures of approximately 80 phlogopite crystals from about 50 different specimens(28 chemically analyzed) were identified. All but five have crystallized with the lJayer monocrinic structure. of these five, three have crystallized as the 2-layer monocrinic polymorph, whereasthe remaining two have crystallized with the 3-layer structure. 2Jayer phlogopites: No. 1062 (o and D)-Madagascar; see Table 1 for analysis and reference. No. 1064 (a and 6)-Madagascar; see Table I for analysis and reference. -Hull, No. 1220 (o) euebec; not analyzed. 3Jayer phlogopites: No. 1261 (b and c)-Madagascar; see Table 1 for analysis and reference. -Labelle No. 1227 (a) Co., euebec; not analyzed. It is noteworthy that three of the non l-layer types are from Mada- gascar' but four other specimensof Madagascar phlogopite crystallized with the common l-layer monoclinic structure (Table 1). The anaryzed- specimen (No. 1261) from Prof. Mauguin consistedof two thin cleavage fragments; specimensNo. 1261 (D and c) x-rayed from one of these have the 3-layer structure, whereasNo. 1261 (o) from the secondfragment has the 1-layer structure. The optical properties of the x-rayed crystals are similar (all essentially uniaxial), and there is probably little differencein their composition. This appears to be analogousto the associationof 1- and 3Jayer lepidolites as described by Levinson (1953). The specimens of known composition that have crystallized as the 2- and 3-layer forms do not appear to be markedly difierent, chemically, from the l-layer types. rn fact, the compositions of all the Madagascar varieties are prac- tically identical. optically, however, the 2-layer varieties differ in having A. A. LEVINSON AND E. WM. HEINRICH their optic planes normal to (010); all l-layer forms have their optic planesparallel with (010). These findings are in qualitative agreement with those of Hendricks mono- and Jefferson(1939), who found 14 phlogopiteswith the l-layer clinic structure and one each with the 2- and 3-Iayet forms. No new poly- morphs of phlogopite have been found in our investigations. Crystals re- ported by Pieruccini (1950) to be triclinic on the basis of goniometric measurements were isolated from a type specimen supplied by him' Weissenberg photographs indicate that the structure is the common l-layer monoclinic form (Table 1). However, written communication with ProfessorPieruccini indicated that two distinct varieties of phlogo- pite are to be found in his specimens,and it is possible, therefore, that we did not r-ray the crystals he believes to be triclinic. The unanalyzed specimensare from widely scattered localities but are predominantly from pegmatites in canada, and from marbles or contact metamorphic deposits in New York and to a lesser extent in Montana and Finland.