Habit evolution of garnets from metamorphic rocks in the Sakar region (SE Bulgaria)

Tzankova, N. 2007. Habit evolution of garnets from metamorphic rocks in the Sakar region (SE Bulgaria). – Comptes rendus de l’Academie bulgare des Sciences, 60, 4, 401-406.

Abstract

An evolution change in the habit type of garnets from the metamorphic rocks in the areas of the villages Orlov Dol, Hlyabovo (along the Yavuz Dere River) and Dervishka Mogila is observed due to the change of P-T conditions during the garnet growth. This habit evolution is assumed on the basis of calculated cation R²⁺/R³⁺ and oxide (FeO+MgO)/(CaO+MnO) ratios for the core and periphery parts of garnet crystals.

In the early stages of growth, garnet crystals form rhombododecahedral type f and type e (rhombododecahedral crystals with small {211} faces), which is transformed later to the type c, represented by equally developed rhombododecahedral and tetragontrioctahedral faces. Numerous rough growth figures, formed on the faces {211} in the process of crystal growth, as well as a relatively smooth surface of faces {110} in combined habit types, support this assumption.

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