Magnesioferrite (Mg, Mn) Fe23+O4 from carbonatites of the Shishimskaya pit in the South Urals

The first data on the composition and physical properties of magnesioferrite from carbonatites of the Shishimskaya pit in the South Urals are presented. The chemical composition and features of the distribution of mineral inclusions in it were investigated using a microanalyzer and Raman spectroscopy, its diagnosis was confirmed by a diffractogram. The mineral was found in the eluvial grus at the outcrop of one of the carbonatite dikes, a cutting rock of the exocontact gabbro zone. Magnesioferrite differs from magnetite in the presence of significant amounts of MgO (up to 14.1 wt. %) and MnO (up to 7.6 wt. %). It composes highly magnetic octahedral crystals 0.3-3.0 mm in size and very small inclusions in spinels and perovskite. Magnesioferrite contains microinclusions of perovskite, hematite, spinel, chlorite, and calcite. For diagnostic purposes, the Raman spectra of magnesioferrite are the most informative. The ideal form of its crystals is similar to metacrystals. The morphological features of the crystals, the absence of possible «shadows» of protominerals in the magnesioferrite, the compromise boundaries of the crystals of magnesioferrite and calcite are all evidence of the simultaneous formation of these minerals, without traces of replacing them with each other. The predominantly calcite composition of the rock, its occurrence in the form of dikes and veins in a diverse substrate, suggest that its minerals were formed during the crystallization of the carbonate melt.