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.
Mineralogical Zoning in a Scapolite-Bearing Skarn Body on San Gorgonio Mountain , California
Concentrically zoned skarns on Mt. San Gorgonio have been studied in detail from the point of view of field and petrographic relations. The skarns are mineralized blocks of marble of the Precambrian San Gorgonio Igneous-Metamorphic Complex, which are within the contact zone between the Complex and the Middle Jurassic Cactus Quartz Monzonite. They consist of cores of calcite-forsterite-diopside marble, surrounded by concentric zones of diopside, actinolite * epidote * calcite + quartz, epidote + garnet * calcite * quartz, and scapolite + calcite + quartz. The genesis of the skarns involved three steps. (l) Regional metamorphism formed tremolite and forsterite from calcite, dolomite, and quartz. (2) The intrusion of the quartz monzonite stabilized diopside * forsterite relative to tremolite * calcite. Reaction between quartz monzonite and marble resulted in the formation of a zone of diopside * wollastonite and a zone of sodic scapolite, by the diffusion of Ca, Mg, and Si across the original contact. Components rejected from this zone formed ferroan diopside in the scapolite zone and in the quartz monzonite, and altered the scapolite to a more calcic form. This process involved a net volume loss of 56.6 percent. (3) Inf i l t rat ion of f luids, possibly of magmatic origin, formed epidote and garnet from scapolite, and actinolite from diopside.
On the use of the Hardening Soil Small Strain model in geotechnical practice
This article highlights the importance of using advanced constitutive soil models in numerical modelling as daily geotechnical practice. In this context, the Hardening Soil (HS) model is presented as the most advanced soil model implemented in the ZSoil finite element code. The article recalls the basic features of the HS model and it explains their role in numerical simulations. The role of pre-failure non-linear behaviour of soils is also discussed. An application of the HS model is illustrated on typical geotechnical problems such as retaining wall excavation, tunnel excavation and undrained loading followed by consolidation.