Studies of Celadonite and Glauconite GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-F Studies of Celadonite and Glauconite By MARGARET D. FOSTER SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 614-F A study of the compositional relations between celadonites and glauconites and an interpretation of the composition of glauconites UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HIGKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S- Government Printing Office Washington, D.C. 20402 - Price 40 cents (paper cover) CONTENTS Page Abstract.-_ ____-____-_--__-_-___--______-__-_______ Fl Interpretation of glauconite coniposition___-___________ F13 Introduction.______________________________________ 1 Relation between trivalent iron and octahedral aluminurn____________________________________ 13 Selection of analyses and calculation of atomic ratios___ 2 The Fe+3 :Fe+2 ratio_______________________ 13 Relation between the composition of celadonites and Relation between iron and potassium____________ 14 glauconites_ _ ___________________________________ 3 Fixation of potassium___________________________ 14 High potassium celadonites and glauconites-_______ 7 Deficiency in potassium content-_________________ 14 Relation between glauconite composition and geo­ Low potassium celadonites and glauconites_________ logic age_____________________________________ 15 Relation between Si, R+2 (VI), Al(VI), and R+3 (VI)_ References cited.___________________________________ 17 ILLUSTRATIONS FIGURE 1. Chemical composition of representative celadonites and glauconites having more than 0.65 atom of potassium per half cell___________________________________________________ F8 2. Relation between Si+R+2 (VI) decrease and A1(IV) + R+3 (VI) increase in high potassium- high charge celadonites and glauconites_____________-_____-___-__-»__-____-__---___ 10 3. Relation between decrease in Si and decrease in R+2 (VI) in high potassium-high charge celadonites and glauconites_____________________________________________________ 10 4. Relation between increase in Al(IV) and increase in R+3 (VI) in high potassium-high charge celadonites and glauconites__..____________________________________________________ 10 5. Relation between excess of R+2 (VI) decrease over Si decrease and layer-charge deficiency-- 13 6. Relation between Fe+3 and Al(VI) in glauconites____________________________________ 13 7. Relation between total iron and potassium in glauconites__________________ __________ 14 8. Extreme and average compositions of Cretaceous and Tertiary glauconites-______________ 16 TABLES Page TABLE 1. Chemical analyses of celadonites, together with their calculated atomic ratios _________ F4 2. Chemical analyses of glauconites having more than 0.65 potassium atom per half cell, together with their calculated atomic ratios___-__-_____-__--_----~-_-----_--__-_--_ 5 3. Chemical analyses of glauconites having less than 0.66 potassium atom per half cell, to­ gether with their calculated atomic ratios_________________-__----_-_-_-__-___-__-_- 6 4. Range and median values of principal constituents in high potassium celadonites and glauconites___________________________________________________________________ 6 5. Range and median values of principal constituents in low potassium celadonites and glau­ conites^ ______________________________________________________________________ 7 6. Al(IV)R+3 (VI) replacement of SiR+2 (VI) in high potassium-high charge celadonites and glauconites-____________________________________________________________________ 11 7. A1(IV)R+3 (VI) replacement of SiR+2(VI) in high potassium-low charge glauconites-______ 12 8. A1(IV)R+3 (VI) replacement of SiR+2 (VI) in low potassium celadonites and glauconites__ __ 12 m SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY STUDIES OF CELADONITE AND GLAUCONITE By MARGARET D. FOSTER ABSTRACT of the specific environment, with the iron content of the glauco­ nite reflecting the degree of iron richness of the environment. A study based on 10 analyses of celadonites and 19 analyses A low potassium content may indicate immaturity, or laclr of of glauconites having high contents of potassium (more than time for more complete fixation of potassium, if it is accom­ 0.65 ion per half cell) shows that both range widely in content panied by high layer charge; or it may indicate degeneration, of trivalent iron and octahedral aluminum, which seem to bear oxidation with attendant loss of layer charge and interlryer a reciprocal relation to each other. The relations among Si, cations, if the layer charge is relatively low. R+3 (VI), Al(IV), and R+3 (VI) indicate that these micas belong The great range in composition of Cretaceous and Tertiary to an isomorphous replacement series that starts with the gener­ glauconites suggests that factors such as specific environment alized theoretical tetrasilicic dioctahedral end-member, of development, opportunity for potassium fixation, and ex­ posure to oxidation are of greater importance in determining [(RJ5 Ra)Siw010 (OH) a].Ki.0, the composition of a glauconite than the geologic age in which and that is characterized by coupled replacement of Si and R+2 it was formed. (VI) by Al(IV) and R+3 (VI). In this series, celadonites, with INTRODUCTION Si ranging from 4.00 to 3.75, stand closest to the end-member, and represent lesser degrees of replacement than the glauconites, The relation between celadonite and glauconite is a in which Si ranges from 3.80 to 3.55. Celadonites and glauconites subject of continuing controversy. A comparative study having fewer than 0.66 potassium ion per half cell belong to the of 10 analyses of celadonite and 40 analyses of glauconite same replacement series, and are similar in layer composition by Hendricks and Ross (1941) confirmed the close com­ to the high potassium celadonites and glauconites. Because positional relationship between the two minerals. How­ celadonites and glauconites have the same crystal structure, are very similar in chemical composition, and are near members of ever, they recommended (p. 708), retention of both the same replacement series, optical, X-ray, and thermal data names, as "the well established term 'glauconite' is used at present contribute little to their differentiation. for a mineral of characteristic sedimentary or'^in In many celadonites and glauconites the decrease in R+2 (VI), whereas the term 'celadonite' is used for a mineral of compared to the theoretical end-member, is greater than the quite different occurrence and paragenesis." Later decrease in Si, and the increase in R+3 (VI) is greater than the increase in Al(IV). The fact that the excess of R+2 ( VI) decrease workers, on the basis of optical, X-ray, and thermal over Si decrease usually agrees closely with the excess of R+3 data, as well as chemical analyses, have maintained that (VI) increase over Al(IV) increase strongly suggests oxidation these minerals are identical. Schuller and Wohlmann of bivalent iron to trivalent. The further fact that the excess (1951), on the basis of a single analysis of a celadonite, of R^tVI) decrease over Si decrease also agrees closely with concluded that the composition of celadonite was near the layer charge deficiency, as compared with a charge of 1.00 per half cell (the layer charge of the theoretical end-member) that of glauconite, except that silicon is partially re­ seems to suggest that originally all these celadonites and glau­ placed by trivalent iron in celadonite and by aluminum conites had layer charges close to 1.00, but that oxidation has in glauconite. As their X-ray spacings were similar, reduced the layer charge by an amount equivalent to the bi­ they suggested their identity. A study of minerals from valent iron oxidized. Karadagh, Crimea, convinced Savich-Zablotzky (1P54) The lack of correlation between iron and potassium in glau­ that the names "celadonite" and "glauconite" refe1" to conites suggests that glauconitization is made up of two separate, the same mineral, their only difference being mod^ of unrelated processes, incorporation of iron into the octahedral layer, and fixation of potassium in interlayer positions, with in­ origin. Malkova (1956), after electron-microscope and corporation of iron preceding complete fixation of potassium. thermal studies of one sample of celadonite, and com­ According to this concept, the amount of iron incorporated into parison of its chemical composition with that of seven the glauconite structure is dependent on the iron concentration other celadonites and glauconites, concluded that cela- F2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY donite and glauconite are identical and suggested that a few from more recent literature. These analyses made the name "celadonite" be reserved for ferruginous by classical methods are considered more reliable for a varieties, and that aluminous varieties be called skolite, study of this kind than analyses made on very small discarding the term "glauconite" entirely. Lazarenko samples (less than 50 mg) by a combination of micro- (1956) also considered celadonite and glauconite iden­ chemical, spectrochemical, and colorinietric methods. tical, and, on the basis of electron micrographs, and The inaccuracy of the later analyses is indicated by their X-ray, optical, and thermal data, placed glauconite, totals ranging, for example, from 98.78 to 102.34 in celadonite, and skolite in the hydromica group.