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

Abstract

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.