Hematite after Magnetite

specimen number:
2072361

location:
Cerro de Mercado, Durango, Mexico

description:
Octahedral crystals of what were once magnetite measuring to 2.2 cm in size, these now replaced by hematite, across the front of this matrix. Classic material for this Mexican locality.

The Cerro de Mercado Mine, located on the northern outskirts of Durango City, Mexico, is a world-class iron deposit situated within a prominent hill of the same name. Geologically, the site is a classic example of an iron oxide-apatite (IOA) or Kiruna-type deposit, where massive bodies of magnetite formed through magmatic-hydrothermal processes during the Tertiary period. The mine is famous among mineralogists for its remarkable pseudomorphs of hematite after magnetite, traditionally referred to as martite, which occur as sharp, lustrous octahedral crystals that often retain the magnetic properties of the original mineral. Historically, the outcrop was first noted by Spanish explorers in 1552, who initially mistook the mountain of iron for silver. Large-scale industrial mining and quarrying began in the early 20th century, specifically around 1900, to feed the burgeoning Mexican steel industry. As of 2026, the Cerro de Mercado remains a significant active open-pit operation and is widely celebrated for producing some of the world's finest examples of martite crystals, frequently found in association with yellow-green fluorapatite.

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