Dioptase

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Lustrous blocky crystals of emerald green dioptase to 0.7 cm in size on matrix. Slight damage present, still very nice. Minor malachite is present.The Ntola Mine, situated within the Mindouli district of the Pool Department in the Republic of the Congo, forms part of a historically significant polymetallic mineralized region. Pre-colonial and ancient local populations actively worked the area for copper since at least the medieval period, followed by formal industrial extraction introduced by European colonists during the early twentieth century. Geologically, the deposits are situated within the Niari basin, where hydrothermal and supergene processes formed complex copper, lead, and zinc occurrences. The geology is characterized by mineralized solutions circulating along the faulted contact between permeable sandstones and karstic limestones, which created an environment favorable for the deposition of secondary metal carbonates and silicates. Modern operations and artisanal workings at the site have become especially famous among mineral collectors for yielding world-class specimen material, most notably intense emerald-green crystals of dioptase associated with other secondary copper minerals such as malachite and plancheite.