Vivianite

Real mineral · uncommon · Fe₃(PO₄)₂·8H₂O

Iron phosphate hydrate that forms colourless when fresh but rapidly turns blue-green upon oxidation of ferrous to ferric iron. Found encrusting fossils in clay deposits. Crystals darken progressively with exposure to light.

Identity

Formula

Fe₃(PO₄)₂·8H₂O

Chemical class

phosphate

Also known as

Blue ocher (earthy form)

Crystallography

Crystal system

monoclinic

Habits

prismatic, massive, earthy

Fracture

fibrous

Physical properties

Mohs hardness

1.5

Density

2.68 g/cm³

Luster

vitreous, pearly

Colors

blue, blue-green, green, colorless (fresh)

Streak

blue to white

Transparency

transparent, translucent

Geology

Origins

sedimentary, hydrothermal

Host rocks

clay, peat, alluvial deposits

Associated minerals

Pyrite, Siderite, Calcite

Geography

Bolivia, Germany, USA, Russia, Romania

Classification

Rarity

uncommon

Gem quality

No

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