Hercynite Research Articles

Introducing Semi-gem quality blue corundum from the Alvand complex, Hamedan, west Iran

Semi-gem quality corundum crystals are formed in a syenite pegmatite dyke in the Alvand igneous-metamorphic complex in west Iran. The dyke is intruded the igneous rocks and the surrounding hornfelses. Corundum is mainly associated with K-feldspar in the rocks and makes crystals 2 to 60 mm across. It shows gray, bluish-gray, pale blue, ink blue and dark blue colours. The crystals show colour zoning and trapiche-like zoning in hand specimens and under the microscope. The main mineral phase inclusions in corundum crystals are muscovite, phlogopite, hercynite and Nb-Ta oxides. LA-ICP-MS and electron microprobe analyzes indicate wide range of Fe/Mg, Fe/Ti, Ti/Mg and Ga/Mg ratios for the analyzed crystals while variation of Cr/Ga ratio is limited. The high Fe and Ga and low Mg and Cr contents suggest a magmatic origin for these corundums. Ti content was found as the main factor controlling the colour.

Analisi archeometriche e statistiche per la caratterizzazione di produzioni di bucchero

The aim of this paper is to provide an update to the debate concerning the production technology of bucchero pottery, as well as presenting new data on the use of raw material for its manufacture and the temperatures of firing. This interdisciplinary research focused on a period of technological changes in bucchero production during the sixth century BC, by applying a quantitative analytical approach using X-Ray powder Diffraction (XRD), X-Ray Fluorescence (XRF), Thermogravimetric Analysis and Differential Thermal Analysis (TG-DTG), and multivariate statistical analyses. A series of samples from northern Etruria (mainly the area of Volsinii) were compared with products from Veii, Ardea, Segni and Pompeii. XRF and XRD analyses provided quantitative results, statistically analysed, concerning the use of raw material, both calcareous and non-calcareous, and the technology of firing where temperatures reached 950°C or above. TG analysis proved that the black surface of bucchero was due to reduced iron oxides and the presence of carbonaceous material on the surface. However, XRD results demonstrated that firing occurred at a high temperature and the ratio between aluminium and iron in the samples led to the formation of hercynite, an iron-aluminate spinel. The results of the study show that during the sixth century BC the changes in technology to obtain a quality bucchero production were related to a sufficiently long soaking period at a high temperature in a reduced atmosphere, regardless of the presence of calcite in the source material.

Synthesis of Hercynite at Very Mild Condition

Synthesis of Hercynite at Very Mild Condition

Occurrence state of SiO2 in hercynite synthesized by reaction sintering

Sample was prepared using Fe2O3, Al2O3 and Si O2 powders as raw materials according to mass ratio Fe O:Al2O3 of 40.8:59.2 and adding a percent of Si O2 in the synthetic system, and being sintered under high purity nitrogen atmosphere at 1 600 ℃for 4 h. The sample was analyzed and characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy and transmission electron microscope. Based on Fe O-Al2O3-Si O2 ternary phase diagram, the existence of silicon dioxide was investigated. The results indicate that silicon dioxide didn't enter into hercynite crystals, but existed among hercynite crystals as amorphous phase. When a percent of Si O2 was added into the synthetic system, amorphous phase containing Si O2 was discontinuously distributed and the direct contact among hercynite crystals wasn't changed.

SOLID SOLUTION, SUBSOLIDUS REDUCTION AND COMPOSITIONAL CHARACTERISTICS OF SPINELS IN SOME APOLLO 15 BASALTS

Compositional data for spinels in the chromite‐hercynite‐ulvöspinel system from three large basalts and for spinels in 48 basalt particles in four soil samples show: (1) that the range of compositions are comparable to those of spinels in Apollo 12 basalts; (2) that the spinel series is complete between 0.75 FeCr2O4 0.25 FeAl2O4 and Fe2TiO4; (3) that the Apollo 12 bimodal distribution is present insofar as chromite‐rich and ulvöspinel‐rich phases are more commonly present than compositions intermediate between these two end members; (4) well defined ionic relationships exist for those cations displaying high octahedral site preference energies in the spinel structure (viz. Cr vs Al and Ti vs Cr+ Al); (5) cations displaying low site preference energies (Fe2+, Mg) show poor correlation; and (6) the absence of a simple relationship between the divalent ions (Fe2+ and Mg), and the paucity (10% of 356 analyses) of intermediate compositions suggests a strong dependence on the structural stability of intermediate members of a normal (hercynite, chromite) — inverse (ulvöspinel) solid solution series