Scapolite : alkali atom configurations , antiphase domains , and compositional Yariations
Electrostatic energy calculations on an intermediate scapolite indicate that Na+ should prefer to be adjacent to Clanions and Ca2* to be adjacent to CO3radicals. The calculations also indicate that short-range ordering of NarCl and CaaCO3 clusters is energetically favored and might give rise to antiphase domains. Electrical neutrality considerations on the anion/radical site in scapolite suggest that the unusual compositional variations observed in the marialite-meionite series are the result of crystallographic constraints on the two possible independent exchange reactions in scapolite: NaCICaCO-3 and NaSie6-Ai. The compositions of naturally occurring scapolites may be explained in terms of the scapolite composition that represents local charge balance between Ca2*, Na* cations and Cl-, COIanions.
Electron-gas theory of ionic crystals, including many-body effects
The electron-gas theory of ionic crystals is extended to include nonadditive (many-body) interactions arising from the simultaneous overlap of the densities of several ions. The theory is used to predict equilibrium geometries, lattice energies, and pressure-induced phase transitions for the fluorides and oxides of the alkali and alkaline earth metals. The results are in good agreement with electron-gas calculations assuming additive, two-body interactions between pairs of ions. This comparison shows that the simultaneous overlap of three or more ions has only a small effect on these crystals, and that for many purposes the simpler two-body approximation is adequate. The predictions of lattice distances and energies agree with experiment to a typical accuracy of 1 or 2%. In order to obtain this accuracy, it is necessary to calculate the electron densities for the anions in a stabilizing potential well whose size is determined self-consistently by the electrostatic potential of the crystal at the anion site. This shrinkage of the anion by the crystal is also a kind of many-body interaction, but it can be handled within the framework of an effective two-body interaction involving the stabilized anions. The corresponding cation expansion effect is also calculated, and shown to be negligible for the alkali and alkaline earth metal ions.
Transverse Ranges Province: A Unique Structural-Petrochemical Belt across the San Andreas Fault System
The San Gabriel and San Bernardino mountain ranges of southwestern California, and associated mountains and basins westward to the Pacific Ocean, make up a unique east-trending geomorphic, stratigraphic, petrologic, and structural belt 400 km long that is offset only a few tens of kilometers right laterally by northwest-striking faults of the San Andreas type. Spot correlations across these faults, suggesting displacements of hundreds of kilometers, perhaps have other explanations. Within the transverse ranges and basins, the east trend is shown by the general petrology, the crystalline rock patterns, pre- and post-batholithic structural features, and batholithic chemical patterns. The east-west unity is especially striking west of the San Andreas fault, but it is also evident in the central and southern San Bernardino Mountains, east of that fault. The Salton Trough and the southern boundary of the Transverse Ranges Province appear to be the most important provincial boundaries in southwestern California. West of the San Jacinto fault, which is just southwest of the San Andreas fault and nearly parallel to it, the Transverse Ranges Province is bounded on the south by the Malibu Coast–Cucamonga fault zone. At and just east of the San Jacinto fault, the southern boundary fault zone is displaced by faulting 30 to 40 km to the southeast, and is continued as the Banning fault. East of the eastern (Mission Creek) branch of the San Andreas fault, east-trending faults are present, but the San Bernardino Mountains rocks and structures merge into the southeast-trending Little San Bernardino Mountains.