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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 54, PP. 1305-1374, 28 FIGS. SEPTEMBER I, 1943 PACKING IN IONIC MINERALS BY H . W. FAIRBAIKN CONTENTS Page Abstract.................................................................................................................................... 1306 Introduction............................................................................................................................ 1307 Acknowledgments.................................................................................................................. 1308 Concept of packing index.................................................................................................... 1308 Development of methods of volume determination.............................................. 1308 The packing index......................................................................................................... 1310 Sources of error.............................................................................................................. 1311 Selection of ion radii..................................................................................................... 1311 Degree of accuracy of packing index........... ............................................................ 1315 Correlation of crystal packing with packing of uniform spheres..................... 1316 Mineralogic correlations of packing index........................................................................ 1320 Correlation of refractive index and density with packing index........................ 1320 Introduction........................................................................................................... 1320 Discussion of data................................................................................................ 1322 Correlation of hardness with packing index............................................................ 1331 Introduction........................................................................................................... 1331 Discussion of data................................................................................................ 1335 Conclusion............................................................................................................... 1345 Correlation of packing index with polymorphic phases........................................ 1347 General statement................................................................................................. 1347 Thermal inversion (fixed composition)............................................................. 1347 Thermal inversion (variable composition)....................................................... 1347 Pressure inversion................................................................................................. 1348 Correlation of packing index with phases showing incongruent melting......... 1349 Correlation of packing index with size of minor ions............................................ 1350 Summary of mineralogic correlations........................................................................ 1353 Geologic aspects of ion packing.......................................................................................... 1353 Introduction................................................................................................................... 1353 General correlation with temperature of formation of minerals........................ 1354 Correlation with silicate crystallization.................................................................... 1355 Correlation with incongruent phases in magma..................................................... 1356 Rock density and rock-packing index...................................................................... 1357 Packing index of metamorphic rocks........................................................................ 1361 The eclogite problem.................................................................................................... 1363 Glaucophane schist....................................................................................................... 1364 Correlation of packing index with thermal and stress environment of meta­ morphic silicates.................................................................................................... 1365 Correlation of packing index with morphological development of porphyro- blasts........................................................................................................................ 1369 Correlation of packing index with rates of mineral alteration........................... 1370 (1305) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/54/9/1305/3440684/BUL54_9-1305.pdf by guest on 25 September 2021 1306 H. W. FAIRBAISN----PACKING IN IONIC MINERALS Page Possible inversions in stony meteorites.................................................................... 1372 Summary of geologic applications............................................................................. 1372 References cited...................................................................................................................... 1373 ILLUSTRATIONS Figure Page 1. Contrast of type of packing and closeness of packing......................................... 1311 2. Relative diameters of selected ions........................................................................... 1315 3. Range of packing indices............................................................................................. 1316 4. Atomic number—ion refractivity relations............................................................. 1321 5. Packing index—density—refractive index relations of Al-rich silicates............ 1325 6 . Packing index—density—refractive index relations of K-rich silicates............ 1327 7. Packing index—density—refractive index relations of Ca-rich silicates........... 1327 8 . Packing index—density—refractive index relations of Na-rich silicates.......... 1329 9. Packing index—density—refractive index relations of Mg-rich silicates.......... 1329 10. Packing index—density—refractive index relations of miscellaneous silicates. 1330 11. Packing index—density—refractive index relations of unclassified silicates.. 1331 12. Packing index—density—refractive index relations of oxides............. 1332 13. Packing index—density—refractive index relations of sulphates, phosphates, chlorides, fluorides.................................................................................................... 1333 14. Packing index—density—refractive index relations of carbonates, nitrates, borates, tungstates, nonionic minerals.................................................................. 1334 15. Packing index—hardness—bonding index relations for chlorides, oxides and hydroxides................................................................................................................... 1337 16. Packing index—hardness—bonding index relations for ZO4 silicates............... 1338 17. Packing index—hardness—bonding index relations for Z2O7, Z 0 3, Z4On silicates 1339 18. Packing index—hardness—bonding index relations for Z}Os(?), Z4O10 silicates 1340 19. Packing index—hardness—bonding index relations for Z 02 silicates and mis­ cellaneous phosphates................................................................................................ 1341 20. Packing index—hardness—bonding index relations for carbonates ,tungstates, sulphates....................................................................................................................... 1342 21. Packing index—density relations of common igneous rocks............................... 1358 22. Chemical relations of selected constituents of rocks of Figure 23..................... 1359 23. Packing index—density relations of an approximately isochemical rockseries 1360 24. Packing indices of common metamorphic rocks.................................................... 1362 25. Comparison of packing indices of minerals in gabbro and eclogite, hornblende schist and glaucophane schist.................................................................................. 1363 26. Packing indices of metamorphic minerals based on thermal characteristics.. 1366 27. Relation between packing and bonding indices and position in “crystallo- blastic” series.............................................................................................................. 1368 28. Comparison of packing indices with rate of mineral alteration......................... 1371 ABSTRACT An attempt is made to give approximate quantitative values to the ratio ion volume/unit cell volume for a selected group of about 200 minerals. A “packing index” is proposed to express this relationship. The general correlation of this pack­ ing index with specific gravity, hardness, and mean refractive index, whereby in­ crease or decrease in one is paralleled by changes in the same direction in the others, is shown in some detail. Unexplained discrepancies in this correlation are Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/54/9/1305/3440684/BUL54_9-1305.pdf by guest on 25 September 2021 ABSTRACT 1307 mostly confined to refractive index data for minerals containing much Ti*+, Zr4+, B3+, Fe2+, and K1+. Ti4+ is likewise dominant in certain minerals with unex­ plained hardness anomalies. These correlations demonstrate the superiority
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