Iron is quite rare in its elemental state at the Earth's surface.  In the presence of oxygen, iron turns to rust (iron oxide).  Many meteorites that fall to Earth from the asteroid belt are composed of native iron (plus impurities).  Very few localities on Earth have native iron of terrestrial origin.  These occurrences are along natural smelting zones, where magma or lava has come in direct contact with coals or other carbonaceous sedimentary rocks.  In such smelting zones, reducing conditions are created, and metallic iron can crystallize.  Famous localities where this has happened include Disko Island in Greenland and the Siberian Traps Flood Basalt Province.


Iron has a metallic luster, silvery-gray color, is somewhat hard (H = 4 to 4.5), is strongly magnetic, has no cleavage, is malleable, and is moderately heavy for its size.  Native iron is always alloyed with nickel in meteorites.  In terrestrial iron occurrences, the Fe is also alloyed with a little Ni.


Native iron in basalt (cut surface, 1.5 cm across) from the Putoran Plateau of Siberia.  Vesicle-filling iron (silver) in basalt/dolerite (black - contains labradorite plagioclase feldspar & bytownite plagioclase feldspar & pyroxene).  Available chemical information indicates that the metal is about 94% Fe, 4% Ni, plus impurities.

The Siberian rock shown above formed during the largest outpouring of flood basalt in Earth’s history.  The Siberian Traps Flood Basalts erupted through crustal fissures as the large head of a new hotspot (mantle plume) surfaced.  This happened at Permian-Triassic boundary times (~251 m.y.), and the timing suggests that Siberian Traps volcanism is related to the Permian-Triassic mass extinction in some way.

The Late Paleozoic sedimentary succession of Siberia contains coal beds (as do many Late Paleozoic successions on Earth).  The magmas came into direct contact with the coal beds, forming reducing conditions, and allowed the formation of native iron.



Photo gallery of iron



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