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Cerro del Mercado, Durango, Mexico


The 'Cerro del Mercado', also known as Iron Mountain, rises majestically at the foot of the city of Durango. This mountain has an east to west orientation. It has a triangular base of approximately two kilometres, its western base being smaller at 1.5 kilometres, and a height of between 100 and 150 metres above the plains that surround it. The shape and colour of the mountain are as impressive today as they must have been for Gines Vasquez del Mercado, who was the valiant explorer who discovered and named it. He must have been immensely disappointed when he discovered that his mountain of silver was actually hematite (the base of iron).

The origins of the mineralization of the veins of iron in the Cerro del Mercado date back 350 million years. The process continued until 180 million years ago, when quartzes and crystals were formed in the central area. The iron vein is massively composed of MARTITA, a pseudomorph of hematite, with perfectly preserved crystals of METATITA. It is quite common to find specimens of minerals with fine octahedral crystals of magnetite in earthy matrices of the rocky base.
Apatite is incidental to iron deposits found in some parts of the general mantle. Many of these specimens appear to have been formed subsequent to the creation of the immense iron deposits, during periods of low temperatures and volcanic activity. From this period specimens of calcite, chalcedony, quartz, titanite, opal, hematite, limonite and sepiolite have been found. Sepiolite is a soft white mineral with a paper like appearance. Apatite crystals are appreciated by collectors for their lustrous hexagonal prisms of six or twelve sides terminating in pyramidal forms, and also for their exotic shades of green and yellow which appear to glow with their own light.

ApatiteLuis Lyons photo
ApatiteLuis Lyons photo

The iron mine of Cerro del Mercado is famous for its fine examples of apatite, some of which are of the best quality in the world. These specimens are not only sought after by collectors, but also by the pharmaceutical industry. The pure crystals of apatite are used in certain medications. Incredibly, there are ways to understand the geological processes that formed the minerals in of the earth, as it is possible to date with considerable accuracy from studying the crystals, the thermodynamic events they were submitted to.