Vivianite

specimen number:
2282004

location:
Anloua, Ngaoundere, Cameroon

description:
A loose crystal grouping of dark vivianite. Complete all around.

The Anloua deposit, situated near Ngaoundere within the Adamawa Plateau of Cameroon, is a globally renowned mineralogical locality famous for yielding some of the largest vivianite crystals ever documented. Geologically, the deposit consists of subrecent, swamp-like sedimentary lacustrine basins rich in organic peat, which are surrounded by highly weathered Pliocene to Quaternary alkaline basaltic volcanic rocks of the Cameroon Volcanic Line. The unique chemical environment developed as iron-rich and phosphorus-rich solutions infiltrated these oxygen-poor, humic-acid-rich sediments, inducing the in-situ crystallization of giant, dark green to blue prismatic vivianite bodies, some forming radiating star-like aggregates several meters across. Discovered by chance around 1920 by local farmers, the swampy clay layers were subsequently exploited through systematic, manual excavation operations under French colonial supervision. Commercial extraction of the clays and targeted specimen recovery peaked through the mid-twentieth century and tapered off by the 1960s.

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