Fayalite Crystals From the Slag of an Ancient Smelting Furnace in Volyn Region

Fayalite crystals from ancient slag found in Volyn region were studied. Fayalite constitutes the bulk of the slag, less common phases of silicon oxide (metallurgical glass), iron (magnetite), unidentified silicate phase X and individual detrital quartz grains. Fayalite crystals have a predominantly skeletal (case-like) shape in the slag matrix and a close combination of several different morphological types of polyhedrons in its cavities. They are faceted by pinacoid {010} and prisms {021}, {110} and {120}. The habit of the crystals is prismatic, pinacoidal and pinacoidal-prismatic, they are often elongated along [001]. Most often skeletal are the faces of the prism {021} and pinacoid. The cores — the central parts of fayalite crystals are enriched with inclusions of glass, magnetite and phase X. Zoning and layering of fayalite crystals in the (021) plane were revealed. The surface of fayalite crystals is often decorated with magnetite microcrystals. In the slag matrix, particularly in fayalite crystals magnetite forms cubic crystals and dendrites, and glass forms various xenoforms and also dendrites. The chemical composition of fayalite crystals is relatively homogeneous, the average content of FeO is 68.00 wt.% and SiO2 is 32.00 wt.%. The source for iron smelting and slag production was swamp siderite or hydrogoethite ore, enriched in potassium and phosphorus. The temperature of fayalite crystal formation from slag melt could reach more than 1000 ºC.