Iron Silicide Spherules

Iron silicide has a narrow bandgap semiconductor character. Its magnetic properties are unique, and its electrical resistivity is approximately 10,000 Ohmcm at room temperature.

Iron silicide is a relatively rare mineral naquite. The spherules are found in a variety of geological settings. A study of spherules from two locations shows a high degree of parallels in their morphology and formation processes. This suggests that an unusual formation process may have produced the spherules.

Spherules from the Ala-Tau site and from the Laurel Hills region share a number of similar morphological and compositional characteristics. Smaller Ala-Tau spherules are found as inclusions in limonite nodules. These are usually spherules with a diameter of 2.7 cm. They have an aerodynamic shape similar to australite tektites. However, these spherules are never submillimeter flanged.

The spherules from the Laurel Hills region have a smooth, finely textured surface. They are mainly rimmed with dark particles and have a metallic luster. Large skeletal crystals are present as well. Inclusions in these spherules are enriched in U and Zr.

Although the formation process of iron silicide has not been fully investigated, it is thought that a strong fractionation event occurred. This is supported by the wide range of REE abundances.

Typical spherules from the Ala-Tau and Laurel Hills regions are characterized by a combination of finely textured surfaces and a metallic luster. In addition, a frothy fusion crust is present. Fissures are typically overlaid with splashes of melt from the ablated anterior.

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