New relationships among the low-temperature alkali feldspars were deduced in part and implied in whole by recent crystal structure analyses of low and high albite and consideration of the electrostatic charge distributions in all the known alkali feldspar structures by Ferguson, Traill & Taylor. In general the most stable low-temperature forms are not those most highly ordered with respect to A...

The present study provides an overview of the ice nucleation activity of different feldspars varying in their chemical composition and crystal structure. In total 15 different feldspars including plagioclase and alkali feldspars were analyzed for one weight percentage using a special freezing array method called μl-NIPI (microliter Nucleation by Immersed Particle Instrument). Additionally, the ...

Fine scale heterogeneities in strontium isotope ratios, 40Ar-39Ar ages, and chemical com~sition have been determined for individual mineral grains and enclaves in the rhyolites of San Vincenzo, Italy. The rhyolites are peraluminous with phenocrysts of alkali feldspar, piagioclase, biotite, and cordierite and have previously been divided into two groups on the basis of whole rock major element c...

At the southernmost part of Tierra del Fuego a few outcrops and erratic boulders of alkali basaltic rocks with ultramafic enclaves have been studied. Alkali basalt plugs or pipes hitherto identified are scarce, and host rocks are constituted by slates that belong to Mesozoic deposition. The petrography, texture and composition of the basalt and xenoliths were investigated by petrographic micros...

Heat capacities (5-380 K) have been measured by adiabatic calorimetry for five highly disordered alkali feldspars (AbeeOr1, Ab65Or15, Ab55Ora5, Ab25Ory5, and AblOree). Positive heat capacity deviations from a linear combination of the end-member heat capacities, which are present mostly at very low temperatures, result in an excess entropy for intermediate compositions. The excess entropy at 29...

Almost all alkali feldspar crystals contain a rich inventory of exsolution, twin, and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions, sometimes multiple. Microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weath...