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The structures of two crystals of Li-bearing fluor-arfvedsonite (1) (K0.32Na0.68)Na-2(Li0.48Fe2.832+Mn0.102+Zn0.06Fe1.463+Ti0.07) (Si7.88Al0.12)O-22[F-1.15(OH)(0.85)] and (2) (K0.25Na0.75)Na-2(Li0.48Fe2.842+Mn0.112+Zn0.05Fe1.453+Ti0.07)(Si7.89Al0.11)O-22[F-1.35(OH)(0.65)] from a granitic pegmatite, Hurricane Mountain, New Hampshire, have been refined to R indices of 1.5(1.6)% based on 1380(1387) reflections measured with MoK alpha X-radiation. The unit cell parameters are (1) a 9.838(4), b 17.991(6), c 5.315(2) Angstrom, beta 103.78(3)degrees, V 913.7 Angstrom(3) and (2) a 9.832(3), b 17.990(7), c 5.316(3) Angstrom, beta 103.79(3)degrees, V 913.2 Angstrom(3). Site-scattering refinement shows Li to be completely ordered at the M(3) site in these crystals. The amphibole composition is intermediate between fluor-arfvedsonite and fluor-ferro-leakeite with a small component (similar to 10%) of fluor-ferro-ferri-nyboite. These amphibole crystals project into miarolitic cavities in a pegmatitic phase of a riebeckite granite. The early-crystallizing amphibole is close to fluor-ferro-leakeite in composition, but becomes progressively depleted in Li and F as crystals project out into miarolitic cavities; the final amphibole to crystallize is a fibrous Li-poor riebeckite. Li plays a significant role in late-stage fractionation involving the crystallization of alkali amphibole in peralkaline granitic environments.

Kornerupine, (square,Mg,Fe)(Mg,Fe,Al)(9)(Si,Al,B)(5)(O,OH,F)(22), contains from 0 to 4 wt% B2O3, and is an ideal material for the evaluation of accuracy and precision of different micro-methods for boron analysis. We have analyzed 32 well-characterized crystals of kornerupine for their B content by SREF (crystal-Structure REFinement), SIMS (Secondary-Ion Mass Spectrometry) and EMPA (Electron-MicroProbe Analysis). The physical phenomena underlying these three analytical methods are entirely different, and hence there should be no systematic errors common to all three methods; this allows evaluation of the accuracy and precision of each method. In the range 0.5-4.4 wt% B2O3, the precisions of the three methods are as follows: SREF (from least-squares refinement) 1-2% relative, 0.01-0.08 wire absolute; SIMS (from reproducibility) 1-2% relative, 0.01-0.08 wt% absolute; EMPA (from counting statistics) 5-22% relative, 0.1-0.2 wt% absolute. Comparison of SREF and SIMS results shows them to agree on average within 3% relative. Hence SREF and SIMS are accurate within the limits of their assigned precision. Comparison of SREF and EMPA results shows a slight systematic difference between the two sets of results, the EMPA values being 7% higher than the SREF (and SIMS) results.

This paper presents new petrological and geochemical data on peridotites and associated pyroxenites from the Zabargad Island (Northern Red Sea), and, particularly, new data on REE bulk rock composition of pyroxenites, and trace element composition of amphiboles (determined by ion probe) from both peridotites and pyroxenites. Results are discussed in the context of field, structural-textural, petrological, geochemical and isotopic knowledge on the Zabargad peridotite. The Zabargad peridotite consists of variably depleted mantle ultramafics. The dominant rock type is a four-phase, granular, spinel(sp)-lherzolite characterized by: i) relative abundance of clinopyroxene(cpx) (15-20% by volume), ii) high contents of fusible components in the constituent minerals, iii) high bulk-rock REE concentrations with Cl-normalized pattern almost flat from H- to MREE, at more than 2 times Cl, and a slight negative LREE fractionation. Other lithologies consist of anhydrous Al-diopside(Di) pyroxenite layers and hydrous (Ti-pargasite-bearing) Cr-Di pyroxenite dykes. Field, petrological and geochemical evidence suggests the following sequence of events developed at mantle depth: 1) Near-solidus evolution of lherzolites and the formation of anhydrous Al-Di pyroxenite layers. The compositional features of the anhydrous Al-Di pyroxenites indicate that they crystallized from tholeiitic melts as garnet-free and garnet-bearing clinopyroxenites, at T higher than 1200 degrees C. 2) Static recrystallization at lower T (and probably P) conditions, most probably around 1000 degrees C. Lherzolites and pyroxenites recrystallized to granular, equilibrium sp-bearing (gnt- and pi-free) assemblages. 3) Widespread kaersutitic amphibole crystallization in equilibrium with the sp-bearing granular association, probably related to infiltration of H2O-rich mantle fluids. 4) Decompression: tectonite-mylonite fabrics were formed along localized shear zones and plagioclase(pl)-bearing assemblages developed in both massive and deformed racks. During decompression, Zabargad peridotites were intruded by hydrous melts which generated amphibole-bearing, Cr-Di websterite dykes, characterized by dominant subhedral pyroxenes with interstitial Ti-pargasite and Ti-phlogopite. Both clinopyroxenes and Ti-pargasites are strongly LREE-enriched, suggesting that these rocks crystallized from alkaline melts. Intrusion was most probably accompanied by circulation of hydrous fluids which produced widespread cryptic and local modal metasomatism (i.e. crystallization of Ti-pargasite + Ti-phlogopite +/- apatite and opaques) in the surrounding lherzolite.