Hematite after Magnetite

specimen number:
2072100

location:
Payun Matru Volcano, Malargue, Mendoza, Argentina

description:
A cluster of what were once large octahedral crystals of magnetite measuring to 3.0 cm in size, these now replaced by lustrous hematite. Minor matrix is attached. This is complete all around and in great condition.

Pseudomorphs are minerals that have replaced an earlier mineral while preserving the original external crystal form, so the specimen retains the shape of one mineral but the composition of another. In the case of hematite after magnetite, the original magnetite crystals are chemically altered through oxidation, with iron being reorganized into hematite while the crystal shape remains unchanged. This process commonly occurs in environments where oxygen rich fluids interact with magnetite, gradually converting it to hematite without destroying the original crystal outlines. As a result, specimens may show the characteristic octahedral form of magnetite but consist entirely of hematite, often with a reddish to dark metallic appearance. These pseudomorphs provide clear evidence of mineral transformation and changing geochemical conditions.

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