Malachite after Azurite with Azurite

specimen number:
8282431

location:
Puit #9, Touissit, Oujda, Morocco

description:

Large thick terminated crystals of azurite measuring to 5.5 cm in length are coming aesthetically off matrix and in the process of being replaced by green crystallized malachite. This is beautiful all around 360 degrees, in perfect condition.

Touissit, located in the Oriental region of northeastern Morocco near the Algerian border, is one of the most significant Mississippi Valley-Type (MVT) deposits in North Africa. Geologically, the mineralization is hosted within Middle Jurassic (Bajocian) dolostones that form part of the Touissit-Bou Beker district. The ore bodies occur as stratabound lenses and replacement structures where hydrothermal fluids deposited primary lead and zinc sulfides, including galena and sphalerite, along with a suite of secondary minerals in oxidized zones. Historically, modern industrial mining at Touissit began in the early 20th century, specifically around 1920, and the district became a major global producer of lead and silver. Large-scale operations continued for several decades under various companies, including the Compagnie Miniere de Touissit (CMT), until the primary ore reserves were largely exhausted and major underground mining ceased in the late 1990s and early 2000s. 

Pseudomorphs from the Touissit area are highly regarded, particularly the striking replacements of malachite after azurite. A pseudomorph occurs when one mineral chemically replaces another while perfectly preserving the original external crystal form (the habit) of the primary mineral. In this specific case, the original sharp, tabular, or prismatic azurite crystals became chemically unstable due to changes in environmental conditions, such as increased hydration or shifting carbonate concentrations in the groundwater. The azurite was gradually transformed into malachite, resulting in specimens that possess the beautiful velvety green color and fibrous texture of malachite but retain the distinct, sharp geometric shape of the former azurite. These "malachite after azurite" specimens are prized by collectors for their aesthetic contrast and for the clear evidence they provide of the complex geochemical transitions that occur within the secondary oxidation zones of copper-rich ore deposits.

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