UDC  549.3  : 523.681.8

Ye.P. Gurov,

V.V. Permiakov,

Institute of Geological Sciences of NAS of Ukraine

55-b, O. Honchara Str., Kyiv, Ukraine, 01601



Language: Russian

Mineralogical journal 2019, 41 (2): 26-33


Chromferide was discovered in impact melt rocks of the El’gygytgyn impact crater. This structure, 18 km in diameter, was formed 3.6 Ma ago in the sequence of cretaceous volcanic rocks in the central part of the Chukotka Peninsula (Russia). Impact melt rocks, glass bombs and shock-metamorphosed volcanic rocks of crater target at the recent erosional level occur in redeposited state in terraces of the El’gygytgyn Lake that occupies the central part of the crater basin. Accessory mineralization of chromferide was discovered by electron-microscopic investigations of impact melt rocks from the lacustrine terrace located in the southern part of the crater. These impactites are massive vesicular clast-rich rocks with partially devitrified glassy matrix and numerous clasts of shock-metamorphosed rocks and minerals. Aggregations and grains of chromferide occur in contraction cracks in rock matrix, and rarely on the inner surface of gas bubbles. Contraction cracks have irregular shape, sometimes they branch out. Chromferide forms intergrowths and separate grains in the cracks, some of its aggregations up to 10 µm long completely fill narrow sections of cracks. The second form of chromferide localization is presented by its crystallization on the inner surface of gas bubbles. Some grains of chromferide have lamellar structure due to their formation in open space. Composition of chromferide corresponds to the Fe3.0Cr0.4 formula, or Fe1.5Cr0.2, and Fe/Cr ratio is ~7. Occurrence of chromferide in contraction cracks and gas bubbles in impact melt rocks is an evidence of its late formation after complete solidification of impact melt rock. Enrichment of impact melt rocks and impact glasses in chromium in comparison with volcanic target rocks of El’gygytgyn crater was previously known from geochemical investigations. Thus, the probable source of chromium in chromferide was the matter of the crater-forming asteroid.

Keywords: El’gygytgyn impact crater, impact melt rock, glassy matrix, gas bubble, chromferide.


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