ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR QUARTERLY PROGRESS REPORT NO0 2 NATURAL MICA STUDIES By E. WM. HEINRICH Project M978 SIGNAL CORPS, DEPARTMENT OF THE ARMY CONTRACT DA-36-039 sc-15357, SC PROJECT NO. 152B-09 DA PROJECT NO. 5-99-15-022 March, 1952

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN QUARTERLY PROGRESS REPORT NOo 2 NATURAL MICA STUDIES INTRODUCTION Research on the natural micas has been expanded along the lines outlined in Quarterly Report No, 1. Many additional specimens have been studied by means of the Weissenberg and powder methods. Complete powder data are now available for all the various polymorphous types in the muscovite-lepidolite series. Their use in connection with studies of finegrained micas and also of micas that appear to fall in the transition areas of the various polymorphs is discussed in detail in this report. Additional Weissenberg studies indicate that the "lithium muscovite" variety of the 2-layer muscovite polymorph reported in the first quarterly report has not been described previouslyo Furthermore investigations on lepidolites with a small 2V have disclosed a new polymorph. High-temperature work has recently been started with the purpose of investigating the effect of heat on crystallization, Apparatus capable of maintaining a constant temperature (within 20-3~) up to about 1200~C9 is being used. This work is as yet in the preliminary stages, The entire mica collection has been renumbered to simplify cataloguing and usage. Henceforth the new numbers will be used. Where it is necessary to refer to micas mentioned in Quarterly Report Noo 1 the old numbers will also be indicated, Selected specimens continue to be prepared for chemical analysis.

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN WEISSENBERG X-RAY STUDIES In Quarterly Report No, 1 (page 9), reference was made to Stevens' analyzed lepidolite No, 1, which was assumed to have the "lithium muscovite" structure on the basis of a high (2o70%) Li20 content. (The structure is illustrated on page 20 of that reporto) Dro S. B, Hendricks, who studied this material by means of x-rays (1939), has graciously supplied some of the original analyzed sample for restudy at this laboratory, Further x-ray work on the material has shown that it crystallized as the normal muscovite polymorpho Thus it was incorrect to assume that Hendricks and Jefferson (1939) had found anything but the normal muscovite polymorph, especially since no reference was made to any irregularities in the Weissenberg photographso Therefore the "lithium muscovite" reported in the first quarterly report is a hitherto unreported variation of the normal muscovite polymorph, "Lithium muscovite" is the variety of the muscovite structure referred to as occurring in Specimen No, 514 (lepidolite M29), which was studied in detail and discussed on pages 6 and 7 of the first report, where it is called "2-layer muscovite type", The following characteristics of "lithium muscovite" illustrate the close structural similarity between it and normal muscoviteo Both haves lo Space group C2/c 2. Cell dimension (approximately) a = 5.2 A b = 9o0 A c = 20,0 A 3 = 950 30 3, 06with todd are present 4o Optic plane perpendicular to (010) They differ in the following points; 1, Indices for "lithium muscovite" are in the normal lepidolite rangeo a = 1.552 ~ = 1,552 t= 1o556 2, Several differences occur in intensities of reflectionso The more important intensity differences for (oke) reflections in normal muscovite and "lithium muscovite" are given belowo The observed intensities of normal _________________________________________ 2 ______________

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN muscovite are those of Hendricks and Jefferson (1959)9 whereas the calculated intensities for muscovite are those of Jackson and West (1930). Normal Muscovite PlaneObserved Calculate "Lithium Muscovite" Observed Calculated 020 w 4 a 022 mw 8 vw 026 a 7 vw 045 a 4 vw 061 w 0 vw 065 vw 0 vvw 066 w 4 Vw 067 vw 0 vvw 069 w vvw This table demonstrates that on the basis of the presence of 06 reflections with dodd, "lithium muscovite" must be considered as having crystallized in a muscovite type of structure, The distortion9 however9 is probably not as great as in normal muscovite, for most of the 06kwith.odd reflections recorded are extremely weak~ This would seem to indicate that "lithium muscovite" is close to the octophyllite micas in structure and composition, for as Hendricks and Jefferson note (19359 page 758) these reflections "are absent for the two-layer biotite-like micas and none is observed for any of the micas that give (hod) intensities of the single-layer structure (except muscovite)"o This variety is apparently found in lepidolites with a low Li 0 content or muscovite with a high Li2O content~ On the basis of this, the varietal term "lithium muscovite" is tentatively proposed. Spectrographic analyses are now being conducted on two micas which have crystallized with this structure. Because Stevens' No0 1, with 2o70% Li 09 has crystallized in the normal muscovite polymorph, it is assumed that lithium muscovite" will have a still higher Li20 content. It is hoped that the extent to which lithium may enter the amuascovite structure will be determined through spectrographic analysis0 _________________________________ 5 ____________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN In this connection, data obtained from x-ray studies of analyze< micas received from Dr. H, PO. Rowledge, Government Mineralogist of Westermn Australia, and Dr. Frans Wickman, Director, Royal Mineralogical Museum of Stockholm, Sweden, are pertinent. Rowledge (1945) has described briefly a dozen micas with their Li20 contentso In about half the cases he also gave the percentages of Na20 and K20, along with optical datao X-ray studies of portions of these analyzed muscovites and "lepidolites" show that these micas have all crystallized as the normal 2-layer muscovite polymorph, Five of the "lepidolites" have lithium contents that range from 2,17% to 2,60% Li2O, This information, coupled with the results obtained from Stevens Noo 1 (2,707 Li2O), substantiates the suggestion that much more lithium may enter the muscovite structure than has been generally realizedo?t Dr. Frans Wickman has supplied lithium micas, mainly from Varutrask9 analyzed by Berggren (1940, 1941)o The optical properties of these micas have been described by Lundblad (1942). The following table presents the results obtained from x-ray studies of these micas. Project No, M978 Swedish Analysis % Li2O Structure Locality 519 A 5o95 6-layer lepidolite Varutrask 520 B 4,35 1-layer lepidolite Varutrask 521 C 359 normal muscovite Varutrask 522 D 2o45 normal muscovite Varutrask 523 E 1o80 normal muscovite Varutrask 524 G 0,75 normal muscovite Varutrask 525 H Oo69 normal muscovite Varutrask 526 I 0,22 normal muscovite Varutrask 528 J 0,76 normal muscovite Varutrask 529 K lo0 normal muscovite Varutrask 530 L 1,1 normal muscovite Varutrask 5531 No 10 4.55 1-layer lepidolite Varutrask 552 No, 13 5.7 normal muscovite Uto 533 No. 14 5o5 6+1-layer lepidolite Rozena From the standpoint of correlating polymorphs with Li20 content | the results obtained from these Swedish micas are not in good agreement with the data obtained from investigations of the lepidolites analyzed by Stevens (see Quarterly Report Noo 1, page 8). The inconsistencies are in the following: No. 519 No, 531 No. 520 No. 532 No. 521 ________________________________ 4 ________________________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Two of the above immediately arouse suspicion. Noss 521 and 532, which are reported to have 359% Li20 and 5.7% Li20 respectively, have crystallized in the normal muscovite structure. As much as 5.7% Li20, or even 3.9% Li20, in the muscovite structure is to be questioned on the basis of present knowledge. It seems possible that the lithium contents of these samples vary so much that the portions supplied represent extreme variations of the analyzed materials, Thus, under such circumstances, any attempt to correlate polymorph with chemistry would be fruitless. At present the compositions of micas 521 and 532 are being redetermined, and further discussion of the Swedish micas must await the new results. The 2V of lepidolites has been reported as varying from 0~ to about 60~~ The vast majority are in the range from 35~ to 60.~ Several occurrences of lepidolite with a very small 2V have been reported, Winchell (1925) describes a sensibly uniaxial lepidolite from Londonderry, Western Australia, and suggests (page 424) that the uniaxial character "may be due to fine twinning on(001)". Axelrod and Grimaldi (1949) report that the 3-layered muscovite polymorph has a variable 2V (35 to 15~) and state (page 559), "Variation in the observed optic axial angle is attributed to the coalescence of the optical effects of superposed twin elements." Hendricks and Jefferson (1939) studied a uniaxial lepidolite from the Western Australia locality and report its structure as the 3-layer rhombohedral polymorph. It is intimately associated with a lepidolite with a large 2V which has crystallized in the 1-layer form. The two types occur in the same sheet and chemical analysis of both sections (Winchell 1925, page 424) are almost identical, Recently Macgregor (1945) has described a lepidolite from Southern Rhodesia with a small 2V, A specimen (No, 539) similar to the described material has been obtained from Dr,, Macgregoro It surrounds a core of muscovite and in turn is enclosed by lepidolite with a large 2V, The muscovite structure is normal, and the mica with a large 2V has crystallized in the 1-layer polymorph, whereas the uniaxial portion has crystallized in the 3-layer rhombohedral form. The association of the 1-layer and 5-layer rhombohedral polymorphs is identical with that of the Western Australia materialo Specimen No, 679 from Usakos, South Africa, obtained from Harvard University (Harvard No, 13879), consists of uniaxial and biaxial segmentso The mica has the appearance of a slightly brownish muscovite, Weissenberg photographs obtained from several crystals taken from the uniaxial section reveal the existence of another 3-layer rhombohedral mica, The biaxial portion, however, has crystallized with the "lithium muscovite" structure. Before assp3 a name (muscovite or lepidolite) to the uniaxial section, it will be necessary to obtain a chemical analysis, or at least a determination of the lithium content o _____________________________ ___. 5 ________________________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN A specimen of lepidolite from Skuleboda, Sweden, (No. 476) was also found to contain a uniaxial section. Again the biaxial part has crystallized in the 1-layer polymorph (space group Cm)0 X-ray studies of the uniaxial portion, however, reveal the discovery of a new 3-layer polymorph, which likewise has crystallized in the monoclinic space group Cm O0-level Weissenberg photographs have been taken about all a- and pseudoa- axes as well as b- and pseudob- axeso A plane of symmetry in the position of b* as well as c was recorded on only one of the photographs; therefore this pattern is considered as having been obtained from rotation about the true a- axis Coupled with information from other Weissenberg photographs, this establishes the crystal system as monoclinico The Weissenberg pattern obtained by rotation about the o-level a- axis is very similar to o-level a- axis photographs obtained from the 3-layer rhombohedral polymorph. The o-level b- axis (Figo 1) and 1-level a- axis (Fig. 2) photographs show some differences. Differences along the 135 reciprocal lattice line between the 3-layer rhombohedral and 3-layer monoclinic may be seen by comparing Fig. 2 with a firstlevel Weissenberg photograph illustrated by Axelrod and Grimaldi (1949, page 569). Indexing showed all reflections with h + k odd and (00.-) with,, / 3n were absent, The possible monoclinic space groups with the information thus far are Cm, C2, and C2/m. In comparing a- and b- axes photographs of the new form and the 1-layer monoclinic lepidolite (space group Cm), a very interesting relationship is observed, When the photographs are superimposed, every third reflection of the new form corresponds exactly with a reflection of the l-layer polymorpho In between, two additional reflections will almost always be found on the photographs of the new polymorpho This relationship also applies to rotation about the pseudo a- and b- axes, Therefore it is logical to assume that the 3-layer monoclinic lepidolite contains the same symmetry elements as the 1-layer polymorph and has also crystallized in the monoclinic space group Cmo The unit cell dimensions are (approximately): a = 5.2 A c = 30o0 A b - 9~0 A B = 91~ (+30') Powder data for the 3-layer monoclinic lepidolite are given in Table 1 and the pattern is illustrated in Fig. 4o POWDER X-RAY STUDIES Before any attempt could be made to study polymorphism in the finegrained micas, it was necessary to obtain powder x-ray data for each of the known polymorphso The only complete powder data on micas found in the literature are for normal muscovite (Nagelschmidt, 1937) and for the 3-layer _______________________ 6 ______________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN muscovite polymorph (Axelrod and Grimaldi, 1949) Grim and Bradley (1951) list partial data for normal muscovite and a single-layer lepidolite and give photographs for the two formso A set of powder pictures was compiled by photographing powdered crystals whose structure had been determined by the Weissenberg methods The set of standard photographs, which includes all known polymorphs of muscovite and lepidolite, is shown in Figs. 3 and 4; and the d-spacings of five forms are given in Table 1 in the appendix. Powder x-ray photographs were taken of approximately 40 specimens, most of which are too fine-grained to study by the Weissenberg method, The photographs were then compared with the standard photographs to determine the type of structure. A complete list of the specimens and their structures may be found in Table 2 of the appendix. All but two of the micas are known formso One of the exceptions is a barium muscovite (described by Bauer and Berman, 19353) the structure of which has not yet been determined; the other is the 3-layered monoclinic lepidolite described in this report. The structure of the fine-grained lepidolites analyzed by Stevens in 1938 (page 8, First Quarterly Report) has been determinedo The complete results are listed below. Stevens ~ Li20 Structure by Project M978 No, Hendricks Weissenberg Powder 2 3.51 too too fine-grained 6-layer plus 2-layer 3 3570 fine- 6 layer 6-layer plus 2-layer 4 3o81 grained too fine-grained 6-layer plus 2-layer 5 3096 too fine-grained 6-layer ( plus 2-layer (?)) The fact that these fine-grained lepidolites are combination forms (Fig, 5) and not single structures confirms the idea that the poor crystal development is in some way related to the chemistryo It is interesting to note that crystals of Stevens Noo 3 large enough for Weissenberg photographs are 6-layer forms, but the poorly developed crystals from the same specimen have a combination 6-layer and 2-layer "lithium muscovite" form, It is probable that the larger crystals have a higher lithium content than the intergrown portionso Specimens 514, 488, 489, 500, 456, and 533 are either 6layer plus 2-layer "lithium muscovite" forms or 6-layer plus 1-layer forms with either the 6-layer or l-layer form dominant, In all cases these specimens are fine-grained and single crystals show poor extinction. With the exception of such fine-grained muscovites as oncosine, the only uncombined pattern obtained was that of the 6-layer polymorpho The 1- or 2-layer "lithium muscovite" form was never found alone in the fine-grained micas studiedo Closer correlation between chemistry and structure will be attempte as soon as the results from quantitative spectrographic analyses are available ________________________________________ 7 _________

BIBLIOGRAPHY 1. Axelrod, J. M., and Grimaldi, F. S., Muscovite with small optic angle: Am. Mineral., 34, pp. 559-572 (1949). 2. Bauer, L. H., and Berman, H., Barium-muscovite from Franklin, N.J.: Am. Mineral., 18, p. 30 (1933). 3. Berggren, Thelma, Analyses ofthe mica minerals and their interpretation. Minerals of the Varutrask Pegmatite. XV.: Geol. Foren. Forh., 62, pp. 182-193 (1940). 4. Some new analyses of lithiumbearing mica minerals. Minerals of the Varutrask Pegmatite. XXV.: Geol. Foren. Forh., 63, pp. 262-278, (1941). 5. Grim, R. E., and Bradley, W. F., in X-ray identification and structures of clay minerals: The Mineralogical Society, London, (1951). 6. Hendricks, S. B., and Jefferson, M. E., Polymorphism of the micas: Am. Mineral., 24, pp. 729-771 (1939). 7. Jackson, W. W., and West, J., The Crystal structure of muscovite - KA12(AlSi3)010(OH)2: Zeit. Krist., 76, pp. 211-227 (1930). 8. Lundblad, Britta, Optical studies of the analysed micas from Varutrask. Minerals of the Varutrask Pegmatite. XXXII.: Geol. Foren. Forh., 64, pp. 55-60 (1942). 9. Macgregor, A. M., Simpsonite and other tantalates from Bikita, Southern Rhodesia: Min. Mag., 27, pp. 157-165 (1945). 10. Nagelschmidt, G., X-ray investigation on clays. Part III. The Differentiation of micas by x ray powder photographs: Zeit. Krist., 97, pp. 514-521 (1937). 11. Rowledge, H. P., The Lithium minerals of the West Pilbara goldfield: Annual Report, Government Mineralogist Analyst and Chemist, Western Australia, for 1943 (1945). 12. Stevens, R. E., New analyses of lepidolites and their interpretation: Am. Mineral., 24, pp. 607-628 (1938). 13. Winchell, A. N., Studies of the mica group: Am. Jour. Sci., (V), 9, pp. 309327, 415-430 (1925). 8

APPENDIX

00 & ~ =-2o120i Fig. 1. 3-layer monoclinic lepidolite O-level b- axis Specimen No. 476. Fig. 2. 3-layer monoclinic lepidolite 1-level a- axis Specimen No. 476. 10

A. B. _ C. Fig. 3 A. Normal muscovite Varutrask, Sweden Specimen No. 525. B. "Lithium muscovite" South Portland, Me. Specimen No. 471a (M-98a). C. 3-layer muscovite Sultan Basin, Wash. Specimen No. 615 (M239).

A. B. Fig. 4I A. 1-layer lepidolite Topsham, Me. Specimen No.'46Tb (M-9)4b). Co Fig. 4 A. 1-layer lepidolite Topsham, Me. Specimen No. 467b (M-94b). B. 5-layer rhombohedral lepidolite Western Australia Specimen No. 978 (M-74). C. 6-layer lepidolite Opportunity pegmatite, Gunnison Co., Colo. Specimen No. 514 a and j (M-29 a and j). D. 3-layer monoclinic lepidolite Skuleboda, Sweden Specimen No. 476a (M-103a).

B- S w;i~iili C. Fig. 5 A. Standard 6-layer lepidolite plus 2-layer "lithium muscovite" Specimen No. 514c (M-29c). B. Stevens No. 2 - 6-layer lepidolite plus 2-layer "lithium muscovite" Specimen No. 976 (M-72). C. Stevens No. 4 - 6-layer lepidolite plus 2-layer "lithium muscovite" Specimen No. 977 (M-73).

TABIE 1 SPACINGS OF POLYMORPHIC FORMS Cu Kl, X = 1.53736 2-layer lithium 1-layer 3-layer rhombohedral muscovite lepidolite lepidolite No. 471 (M-98a) No. 467 (M-94b) No. 978 (M-74) I d spacing I d spacing I d spacing m 9.952 s 9.908 m 9.908 m 5.007 s 4.980 m 4.968 m 4.449 w 4.494 m 4.657 vvw 3.945 vw 4.341 m 3.839 vvw 3.866 vw 4.121 m 3.580 w 3.707 vw 3.861 vs 5.309 w 3.462 s 3.608 s 3.091 ms 3.320 vs 3.333 s 2.861 m 3.208 s 3.074 w 2.651 m 2.976 s 2.867 s 2.571 s 2.841 m 2.675 mw 2.455 w 2.755 s 2.573 mw 2.375 ms 2.571 m 2.468 vw 2.243 m 2.474 m 2.387 vw 2.186 m 2.387 vw 2.253 mw 2.126 vw 2.247 m 2.132 vw 2.052 vvw 2.196 ms 1.988 m 1.984 mw 2.132 vvw 1.956 vw 1.955 m 2.081 w 1.748 w 1.718 vw 1.951 vw 1.715 nw 1.643 w 1.742 m 1.646 w 1.611 vw 1.720 vvw 1.581 w 1.576 m 1.644 vvw 1.544 w 1.547 vvw 1.596 m 1.511 mw 1.511 vww 1.557 vw 1.493 vvw 1.481 vvw 1.510 vvw 1.420 vvw 1.457 w 1.500 vvw 1.375 vvw 1.455 w 1.487 vvw 1.352 vvw 1.411 vvw 1.453 vw 1.337 w 1.341 vw 1.427 vw 1.299 vw 1.295 w 1.340 ww 1.242 vvw 1.285 w 1.296 ww 1.199 vvw 1.269 vvw 1.136 vw 1.243 vvw 1.220 vw 1.199 14

TABLE 1 (cont) 6-layer monoclinic lepidolite 3-layer monoclinic lepidolite (new form) No. 514 (M-29a and j) No. 476 (M-103a) I d spacing I d spacing ms 9.386 s 9.909 m 4.985 m 4.984 m 4.493 m 4.539 w 3.839 w 3.867 -m 3.608 m 3.561 m 3.470 s 3.323 m 3.308 w 3.177 m 3.189 vw 3.109 m 5.070 vw 2.951 m 2.876 vw 2.873 -m 2.775 vw 2.831 vs 2.572 ms 2.604 m 2.416 vvw 2.542 vvw 2.248 w 2.442 wvw 2.190 vw 2.335 vw 2.039 vw 2.257 s 1.985 vw 2.171 -vw 1.684 vw 2.091 vv 1.633 vvw 2.024 vvw 1.572 m 1.986 m 1.506 vw 1.711 vvw 1.395 w 1.667 ww 1.355 vw 1.635 ww 1.319 vw 1.596 w 1.300 vvw 1.551 ww 1.239 w 1.512 vvw 1.416 vww 1.333 vw 1.504 vw 1.283 vvw 1.241 15

TABLE 2 MICAS X-RAYED BY POWDER METHODS Number Structure 450 (M-77) 6-layer lepidolite 456 (M-83) 6-layer lepidolite plus 2-layer "lithium muscovite" 459 (M-86) 6-layer lepidolite 467 (M-94b) 1-layer lepidolite 470 (M-97b) 1-layer lepidolite 471 (M-98a) 2-layer "lithium muscovite" 472 (M-99) 6-layer lepidolite 473 (M-100) 6-layer lepidolite 475 (M-102b) 1-layer lepidolite 476 (M-103a) 3-layer monoclinic lepidolite (new form) 481 (M-247) 2-layer normal muscovite 488 (M-254) 1-layer lepidolite plus 6-layer lepidolite 489 (M-255) 6-layer lepidolite plus 1-layer lepidolite 500 (M-262) 6-layer lepidolite plus 1-layer lepidolite 514 (M-29-1) 6-layer lepidolite plus 1-layer lepidolite (M-29-2) 6-layer lepidolite (M-29-3) 6-layer lepidolite plus 1-layer lepidolite (M-29-c) 6-layer lepidolite plus 2-layer lepidolite,(M-29-a) 6-layer lepidolite (M-29-j) 6-layer lepidolite 519 (M-272) 6-layer lepidolite 520 (M-273) 1-layer lepidolite 521 (M-274) 2-layer normal muscovite 525 (M-278) 2-layer normal muscovite 528 (M-281) 2-layer normal muscovite 529 (M-282) 2-layer normal muscovite 532 (M-285) 2-layer normal muscovite 16

TABLE 2 (cont) Number Structure 533 (M-286) 6-layer lepidolite plus 1-layer lepidolite 534 (M-287) 2-layer normal muscovite 540 (M-292) structure undetermined (barium muscovite) 541 (M-294) 2-layer normal muscovite 542 (M-295) 2-layer normal muscovite 543 (M-296) 2-layer normal muscovite 544 (M-297) 2-layer normal muscovite 545 (M-298) 2-layer normal muscovite 546 (M-299) 2-layer normal muscovite 548 (M-301) 2-layer normal muscovite 550 (M-303) 2-layer normal muscovite 552 (M-305) 2-layer normal muscovite 553 (M-306) 2-layer normal muscovite 813 (M-109) 2-layer normal muscovite 967 (M-55) 6-layer lepidolite plus 2-layer lepidolite 975 (M-71) 6-layer lepidolite 976 (M-72) 6-layer lepidolite plus 2-layer lepidolite 977 (M-73) 6-layer lepidolite plus 1-layer lepidolite 978 (M-74) 3-layer rhombohedral lepidolite 17