Hematite after Magnetite

specimen number:
2133050

location:
Cerro Mercado, Durango, Mexico

description:
The top of matrix is covered by octahedral crystals of what were once magnetite averaging 1.0 cm in size, these now replaced by hematite.

Cerro de Mercado in Durango, Mexico is a large iron ore deposit located near the city of Durango. The deposit is composed mainly of massive magnetite and hematite and has been mined since the 19th century as an important source of iron for Mexican industry. The hill itself is largely made up of iron rich rock and has supplied ore for many years through open pit mining.

A pseudomorph forms when one mineral replaces another while preserving the original crystals external shape. In the case of hematite after magnetite, the original magnetite crystal was chemically altered through oxidation. During this process iron in the magnetite reacted with oxygen and changed to hematite while keeping the same crystal form. The resulting specimen looks like a magnetite crystal but is actually composed of hematite.

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