Vivianite

Vivianite is a hydrated iron phosphate prized by collectors for its dramatic colour. Freshly exposed crystals can be nearly colourless, but on exposure to light and air the iron oxidises and the mineral deepens to a striking blue, blue-green and finally near-black, often in sprays of bladed crystals.

Identifying vivianite

Vivianite is soft (1.5–2) with a perfect cleavage that yields flexible sheets. Its evolving blue-green colour is diagnostic. It forms in oxygen-poor, phosphate-rich settings — in the cavities of fossil shells and bones, in clays and bogs, in some ore deposits and in granite pegmatites.

Where it is found

Notable vivianite comes from Bolivia (large bladed crystals), Cameroon and Brazil, and as blue coatings on fossil ivory and ironstone concretions worldwide.

For collectors

Deeply coloured, lustrous bladed crystals and aesthetic sprays are the prize. Because vivianite is light-sensitive and soft, specimens are best kept out of strong light and handled with care.