Delvauxite

specimen number:
1052801

location:
Chateau de Berneau, Dalhem, Liege, Wallonia, Belgium

description:
A very good example for the species with nodular delvauxite throughout matrix. From the type locality for the species. The specimen comes with an antique label as shown at the end of the video. This label gives an acquisition date in 1914.

The Chateau de Berneau locality, situated near Vise in the Liege Province of Belgium, is historically recognized in mineralogy for its unique secondary phosphate occurrences. Geologically, the site lies within the Carboniferous limestone sequences of the Vise region, which were subjected to localized karstification, brecciation, and hydrothermal alteration. Weathering of local sulfide-bearing and organic-rich sedimentary strata released phosphate and sulfate ions into circulating groundwater, interacting with iron-bearing minerals to form unusual amorphous and crystalline secondary minerals within small fissures and soil pockets. Small-scale quarrying and exploration occurred intermittently in the vicinity during the nineteenth century, driven by geological mapping and mineralogical sampling of the local limestone formations. Active mineral extraction at this specific chateau property was highly limited and sporadic, largely concluding by the late nineteenth century as the site transitioned to purely historical and geological significance.

Delvauxite is an amorphous hydrous iron phosphate mineral that typically forms as a secondary product in the oxidation zones of iron-bearing sedimentary deposits and gossans. Geologically, it precipitates from cold, phosphate-rich meteoric waters that interact with decomposing iron sulfides under surface or near-surface conditions. The mineral is characterized by its dull to waxy luster and yellowish-brown, reddish-brown, or brownish-black coloration, commonly occurring in concretionary, botryoidal, or stalactitic habits. Because it lacks a defined internal crystal structure, it is classified as a mineraloid, frequently found in close association with other secondary species like vivianite and limonite.

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