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Maghemite (Fe 2 O 3, γ-Fe 2 O 3) is a member of the family of iron oxides. It has the same formula as hematite , but the same spinel ferrite structure as magnetite ( Fe 3 O 4 ) and is also ferrimagnetic .
Maghemite differs from magnetite in that all or most of the iron is in the trivalent state (Fe 3+) and by the presence of cation vacancies in the octahedral sites. Maghemite has a cubic unit cell in which each cell contains 32 oxygen ions, 21 1 ⁄ 3 Fe 3+ ions and 2 2 ⁄ 3 vacancies. The cations are distributed randomly over the 8 tetrahedral ...
The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation. Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant, and temperature plays a smaller role.
Mamelon – Rock formation created by eruption of relatively thick or stiff lava through a narrow vent; Mid-ocean ridge – Basaltic underwater mountain system formed by plate tectonic spreading; Pit crater – Depression formed by a sinking or collapse of the surface lying above a void or empty chamber
Maghemite is a polymorph of hematite (γ-Fe 2 O 3) with the same chemical formula, but with a spinel structure like magnetite. Large deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that have still, standing water, or mineral hot springs, such as those in Yellowstone National Park in North ...
Off-Earth, rock can also form in the absence of a substantial pressure gradient as material that condensed from a protoplanetary disk, without ever undergoing transformations in the interior of a large object such as planets and moons.
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A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a geographical region (the stratigraphic column).