Strengite

Strengite is a hydrous iron(III) phosphate mineral with the chemical formula FePO4·2H2O. It is a secondary phosphate mineral that forms in oxidized zones of phosphate-rich iron deposits and as an alteration product of vivianite in sediments or hydrothermal environments. Strengite can develop in veins, cavities, and crusts where phosphate-bearing fluids interact with iron oxides.

In appearance, strengite is typically colorless to white or pale yellow-brown, and it may occur as small crystals, granular masses, or crusts. Crystals, when present, are commonly needle‑like or tabular and may be translucent to transparent. The mineral is relatively soft and is soluble in acids, reflecting its hydrated phosphate composition.

Strengite is found in a number of localities worldwide, often in association with goethite, limonite, jarosite, and other phosphates such as wavellite. It is of interest mainly to mineral collectors and researchers studying phosphate mineralogy and alteration processes in iron-rich environments. The mineral has no established commercial uses, but its occurrence helps illuminate the geochemical conditions that concentrate phosphate in oxidized iron systems.

Stability-wise, strengite is stable under ambient terrestrial conditions but loses water upon heating, converting toward anhydrous iron phosphate forms. Its presence can indicate past oxidative conditions and phosphate availability in the deposit or sedimentary setting.