THE PECTOLITE-SCHIZOLITE-SERANDITE SERIES* Wer,rnuln T. Scn,lr,r,nn, U. S. Geol,ogical Suraey, Woshington25, D. C. ABsrRAcr A study of the pertinent recorded analyses of pectolite, schizolite, and serandite, indi- cates that they are members of an isostructural series from pectolite (4CaO NarO.6SiO: 'H2O or Ca:NaSiaOs(OH)) to serandite (4MnO NazO.6SiO:.HzO or MnzNaSisOs(OH)), another example of a series in which calcium and manganese proxy each other. The only recorded analysis of serandite is that of a calcian serandite. Schizolite is a manganoan pectolite and should not be rated as a species. The specific gravity and indices of refraction for the calcium and for the manganese end members are: Pectolite,Ca:NaSisOs(OH), G : 2.86; a: 1.595, P:1.605, t:1.633. serandite, : 3'32; y:'111t:',??,,1:i":';":"?lt] " IlrrnooucrtoN The pectolite-schizolite-seranditeseries is an example of an isostruc- tural seriesin which bivalent manganese(I.R. 0.80) proxies for calcium (LR. 0.99) at least to an extent of 77 per cent. The calcite-rhodochrosite seriesis even more complete for it indicates "complete ionic substitution of I{n++ to Ca++ in nature." as expressedby Kulp, Kent, and Kerr (1951)or, as stated earlierby Kulp, Wright, and Holmes (1949):"There- fore, it seemsthat the substitution of Ca+ for Mn+ is continuous for rhodochrosite to calcite." These conclusionsconfirm the earlier work of Krieger (1930). The wollastonite-bustamite seriesis another example in which manganese(plus a little ferrous iron) proxies the calcium in wollas- tonite to the extent of at Ieast 70 per cent, with retention of the wollas- tonite structure (Schaller). The maximum contentof MnO*FeO sofar found, in a bustamite from Australia, is about 28 per cent NInO with 8 per cent FeO. Several addi- tional bustamites from other localities contain almost as much manganese and iron (Schaller). For axinite the ratio of CaO to FeO*MnO*MgO was formerly held to be constant (Schaller,1911) but recent studiesby Milton, Hildebrand, and Sherwood(1953) show it to be variable. fn rhodonite and pyroxmangite the amount of calcium proxying for manganeseis variable but always small. The maximum content of CaO in rhodonite is about 11 per cent (Schaller,1938, p. 582). The so-called x Publication authorized by the Director_ U. S. Geological Survey. t022 TH E PECTOLI T E.SCE I ZOLI TE-SERA N DI T E SEKI ES to23 "high lime rhodonites" listed in standard reference books are either bustamite, johannsenite, or a mixture of rhodonite and johannsenite (Schaller, 1938, p. 580). In other calcium-manganeseminerals, such as inesite (Glass and Schaller, 1939) and johannsenite (Schaller, 1938) the content of CaO is constant and calcium and manganesedo not proxy each other. In all three of the series mentioned in which the proxying of man- ganesefor calcium is compJeteor nearly so, the almost manganese-free calcium end member is by far the commonest and most abundant. For those series (rhodonite, pyroxmangite) in which the manganese end member is the commonest and most abundant, calcium seemsto be al- ways minor in amount. That serandite, the manganese richest member of the pectolite- Frc.1. (a) Pectolite; (6) Schizolite; (c) Serandite. schizolite-seranditeseries is a pectolite in which manganeseproxies cal- cium to an extent greater than a 1:1 ratio, was shown by Machatschki (1932). Schizolite is intermediate between pectolite and serandite and the close morphological relationship of the triclinic crystals of schizolite and pectolitewas shownby Peacock(1935) and by Ito (1939). The similarity of the r-ray powder patterns of the three minerals is shown in Fig. 1 and the shifts in the positions of the lines in Table 1. Many pectolites contain small quantities of manganese,as well as iron, though it is believed that the MnO content of the manganpectolite from Magnet Cove, described by Williams (1891) and reported to be 4.25 per cent MnO, is much too high, like the MnO and FeO percentagesgiven by him for the wollastonite and natroxonotlite from Potash Sulphur Springs, Arkansas (Schaller, 1950). That the content of MnO in the manganpectolite from Arkansas is not as high as reported is also indi- 1024 WALDEMAR T. SCHALLER Tanr,r 1, Poworn Dar.q.ron rnn Colp.tnrsoN ol PrcrourE. ScHrzorrro. eNn Srn,qxnrra Pectolite Schizoiite Serandite d I a d I 7.83 7.73 mw /.J) MS /.UJ 6.92 mw 6.75 MS 5.50 J 5.39 mw 5.24 mw 3.90 6 3.85 ms 3.77 ms 3.52 5 3.47 mw 3.38 mw J.JJ 6 3.27 InS 3.19 s 3.10 8 3 .06 InS 3.00 S 2.92 10 2.89 2.85 s 2.74 6 2.69 MS 2.62 MS 2.60 6 2.56 MS 2.51 ms 2.30 6 2.27 MS 2.21 ms 2.17 6 2.r5 InS 2.12 mw s: strong. ms:moderately strong. mw:moderately weak. cated by the value of its specific gravity, namely, 2.845, as given by Williams, which is lower than the specific gravity (2.86) of pectolile free from manganese. X-Rev ParrBnNs X-ray difiraction patterns of these minerals were taken some years ago by W. E. Richmond, formerly of the U. S. Geological Survey, and more recently by Fred A. Hildebrand. The specimensfor which patterns were obtained, are as follows: Pectolitefrom Bergen Hill, NewJersey, U.S.N.M. 82452. Film No. 5502. Manganpectolite from Magnet Cove, Arkansas, U S.N.M. R-3097. Film No. 240. Schizolite from Julianehaab, Greenland, U.S.N.M. 95502. Film No. 5752. Serandite from Los, French Guinea, U.S.N.M. 96515. Film No. 5739. From a comparison of their patterns, C. L. Christ and J. M. Axelrod, of the U. S. Geological Survey, conclude that the same general pattern prevails and that all four samples are isoslructural. The patterns of pectolite and of manganpectolite are identical; those of schizolite and of serandite contain some difierence in line position and line intensity. However, it seemsvery likely that these differencescan be ascribed to the differencesin chemical composition. The patterns for schizolite and for serandite are very similar; their differencesare less than their differ- ences from the patterns of pectolite. But the overall similarity is re- tained and it must be concluded, on the basis of their powder patterns, that pectolite, manganpectolite, schizolite, and serandite form an iso- structural series. T H E P ECTOLI TE-SC H I ZOLI T E-SER,4 N DI T E SERI ES r025 "r1 r\ | ,,' I Y,.' 7 ,l I I e/. /tzL/' '/ // ,/ llit t+v o / ry.' O { 1m B Frc. 2. Variation curves for G (specific gravities) and z (indices of refraction a, B, ,y) for the pectolite-schizolite-serandite series. The values for alpha and gamma are represented by circles whereas those for beta are represented by triangies, so as to avoid confusion. Solid dots represent specific gravities. A. Pectolite. CazNaSiaOs(OH). B. Serandite. Mn:NaSi:Os(OH). The powder data given in Table 1 were kindly furnished by Fred A. Hildebrand and are given here to show the isostructural relationship be- tween pectolite, schizolite, and serandite. Measurementsfor d were made with a ?il..nt.scale and 1 was estimated visually for schizolite and ser- andite. Corrections which would make very minor changesin d were not considered. The patterns of the three minerals shown in Fig. 1 were taken with Debye Scherrer powder cameras (114.59 mm. diameter), FeK" (Mn filter), I:1.93734. 1026 WALDEMAR T. SCHALLER Coruprr,-qrror.IoF PRoPERTTES The available pertinent literature data on the properties of pectolite, schizolite, and serandite are shown in the following compilation (Table 2) and the variation curves for specific gravity and for the indices of refraction are given in Fig. 2. The component weight percentagesare calculated on the basis of the determined values for MnO and FeO. The Ca-component is then obtained by difference.Both the specificgravities and the indices of refraction increase with increasing amounts of man- ganese.The continuous shift of the lines of the r-ray patterns has been given in Table 1. The data are meager and there is little assurancethat the physical properties were always determined on the actual samples analyzed. For example the three analyses of schizolite from Greenland (No. 9 in Table 1) given by Blggild show considerablevariation in the percentages of MnO (9.84,11.69, and 12.90),and correspondto 32, 35, and 40 weight per cent of the calcium-free manganese and iron end members. The specific gravity of the mineral is given as within the range 2.97-3.13. The only indices of refraction of schizolite found in the literature are those given by Larsen (192I) for an unanalyzed specimenin the Harvard collection. The values plotted in Fig. 2 for schizoliteare the averageof the available data. For pectolite, with lessthan one per cent of the calcium-freemanganese and iron end member, Harada (1934) gives the indices of refraction for three analyzed samples (average given in column 3, Table 2). He also gives the indices for three additional samples not analyzed. His values agree very closely with those given in Larsen's Tables. Harada analyzed 1.595 r.604 |.632 1.594 1.603 1.63r 1.595 1.605 r.633 Harada not analyzed 1.595 t.604 1.633 1.596 1.605 1.635 r.594 1.604 7.632 Larsents Tables, 1st ed. 1.595 1.606 1.633(p.118) 1.595 1.606 L(tj[ (p.216) Larsen's Tables, 2nd ed.