Interpretation of the Metamorphic Processes in Various Rock Types Using the Chemistry of Garnets (Selecka Mountain, Macedonia)

The garnets from the complex of Selecka Mountain could be divided in two groups on the basis of their chemical composition and zoning. The garnets from muscovite-schist and amphibole-schist show characteristics typical for a growth in prograde metamorphic conditions up to the medium metamorphic grade. Characteristics of the other garnets (from aplite granite, aplite veins and metabasite) suggest their formation in anatectic or highly metasomatic conditions. The inversion in chemical zoning, observed in some of them, is discussed and related to possible processes of growth

Solid Solution Between Epidote and Hancockite from Nezilovo, Macedonia

A solid solution between the epidote formula and hancockite formula (Pb equivalent of epidote) was found in the “mixed series” of the Pre-cambrian complex in the central part of the Pelagonian massif near the village of Nezilovo. The mineral is determined by optical investigation, X-ray diffraction and microprobe analyses. A thermogravimetric analysis was performed and determined 1.68 wt.% of H2O. Two distinct compositions were found: one with 20-25 mol% and one with about 70 mol% of hancockite component, indicating two different parageneses where the Ca in epidote is partly substituted by Pb

Solid Solution Between Epidote and Hancockite from Nezilovo, Macedonia

A solid solution between the epidote formula and hancockite formula (Pb equivalent of epidote) was found in the “mixed series” of the Pre-cambrian complex in the central part of the Pelagonian massif near the village of Nezilovo. The mineral is determined by optical investigation, X-ray diffraction and microprobe analyses. A thermogravimetric analysis was performed and determined 1.68 wt.% of H2O. Two distinct compositions were found: one with 20-25 mol% and one with about 70 mol% of hancockite component, indicating two different parageneses where the Ca in epidote is partly substituted by Pb

Compositional Zoning in Amphibole from Amphibole Bearing Parageneses of West Psunj (Croatia): Evidence for Progressive Metamorphism?

Amphibole bearing parageneses from the western part of Mt. Psunj (Croatia) record evidence of prograding metamorphism. Optical and microprobe analyses, together with thermobarometric evaluations on amphibole bearing parageneses, show a zonation with Si- and Mg-concentrations decreasing from core to rim along with increasing Al-, Na-, and Ti-content. Changes in the chemical composition of amphibole grains are interpreted through coupled substitutions, and reactions with co-existing minerals during an increase in metamorphic conditions from greenschist to amphibolite facies. The change in P-T conditions recorded in the growth of amphibole grains (general prograding pattern) together with changes in the modal compositions in related parageneses could be interpreted in a model of a subduction zone

Morphology and Crystallo-Chemical Characteristics of the Fe-, Mn-, Mg-, Ca- Carbonates from Zagradje near Busovaca (Bosnia and Herzegovina)

Siderite, ankerite, calcite and aragonite are determined in well known hyalophane contained alpine veins from Zagradje near Busovaca. Siderite (45.3 % FeO) is the early carbonate in paragenesis. Arrangement of {0001}, {113}, {101} and {332} resulted in two types of habit: isometric with characteristic elements of trigonal symmetry and isometric with elements of pseudomonoclinic symmetry. Two ankerite phases are mainly determined through their Mn content (AI-4.30% MnO, AII-1.94% MnO) and their positions in paragenesis. The unit rhombohedron and twin on basal pinacoid are their representative habits. Saddle-shaped rhombohedrons of calcite and aragonite very rich in crystal faces ({110}, {010}, {011}, {021}, {111}, {121}, {031}, {051}, {012}, {032}, {122} and {362}) have been separated among late carbonates. The crystals of aragonite are strongly elongated in the direction of [001] and flattened on (110) and this face is the common twin plane. At the beginning initial solution was very rich in iron which rapidly decreased during crystallization. The solution contained more Fe, Mn and Mg at the beginning of crystallization and more Ca during the final stage. Such a complex solution generated the described carbonates according to their variable solubility. Determined elements confirm the existence of members including manganoan ankerites which are more common than generally thought. According to partial substitutions of Mn for Fe in octahedral sites ankerites would be formulated as; (Ca0.94Mn0.06)(Fe0.48 Mg0.45Mn0.16Sr0.02) (CO3)2 and (Ca0.94Mn0.06) (Fe0.46Mg0.53)(CO3)2

The Ti environment in natural hibonite: XANES spectroscopy and computer modelling

The local atomic structure around Ti in Ti-bearing hibonite (CaAl12O19) was studied using X-ray absorption near-edge structure (XANES) spectroscopy and computer modelling. Structural models of the direct substitution of Al by Ti3+, Al by Ti4+ charge balanced by the coupled substitution of Mg2+ for Al, and small Ti clusters were considered. The Ti K-XANES spectra of natural hibonite with different Ti concentration were recorded. Theoretical Ti K- XANES spectra for structural models of hibonite were calculated. It was shown that the theoretical Ti K-XANES spectra for a model with Ti at the five-coordinated M2 site are in agreement with the experimental XANES spectra of hibonite with low concentrations of Ti, while the theoretical spectra for a structural model of clustered Ti are in agreement with the experimental spectra of hibonite with higher Ti contents

Hedyphane from Nezilovo, Macedonia

Two different members of lead calcium arsenate series of apatite group from Nezilovo are found. According to the chemical formula (calculated on the basis of 10 cations), infra red absorption powder spectra, X-ray powder patterns and unit cell dimensions these are two distinct members of one mineral species. Unit cell dimensions are a=10.157(3), c=7.256(6) and a=10.154(2), c=7.191(3) A. The first sample has Pb:Ca ratio 7.35:2.59 and the second one 6.54:3.45, what is closer to ideal hedyphane formula (6:4)