Vivianite: Properties, Occurrence, Uses
Vivianite, a fascinating mineral known for its vibrant blue-green hues and unique properties. Vivianite is a hydrous iron phosphate, meaning it's a mineral composed of iron, phosphorus, and water molecules. Its chemical formula is Fe₃(PO₄)₂·8(H₂O).
Vivianite was named after Reverend John Vivian, a British mineralogist who discovered the mineral in Cornwall, England, in 1801.
Vivianite was once thought to be the source of the blue color in odontolite, a fossilized bone and teeth material. However, further research has shown that the blue color is likely due to other factors.
 |
| Vivianite crystals From: Morococala Mine, Santa Fe Mining District, Dalence Province, Oruro Department, Bolivia Credit: Anton Watzl |
Where is Vivianite found
Vivianite crystals are often found inside fossil shells, such as those of bivalves and gastropods, or attached to fossil bone. Pure fresh vivianite is colorless, but the mineral oxidizes very easily, changing the color, and it is usually found as deep blue to deep bluish green prismatic to flattened crystals. Vivianite occurs in various geological settings, including:
- Weathered zones of phosphate deposits: This is where Vivianite often forms its most beautiful crystals.
- Granite pegmatites: These igneous rock formations can contain pockets rich in phosphate minerals, where Vivianite can crystallize.
- Clays and sediments: Vivianite can precipitate in sediments rich in organic matter, sometimes replacing fossils and bones.
- Recent alluvial deposits: Vivianite can form in marshes, bogs, and other wet environments where iron and phosphate are abundant.
 |
| Vivianite scepter from Brazil. Photo: Adam Kelly Gems Jewelry |
Vivianite Properties
Composition: Chemical Formula: Fe₃(PO₄)₂·8H₂O (hydrated iron phosphate)
Color: Vivianite displays a captivating blue-green color, though it can also be colorless, greenish-white, or even gray when freshly formed. Oxidation over time deepens the color to a dark blue or blue-green.
Luster: Vivianite exhibits a vitreous to pearly luster, meaning it reflects light like glass or pearls depending on the crystal face and polishing.
Hardness: Vivianite ranks 1.5-2 on the Mohs hardness scale, making it relatively soft and susceptible to scratches.
Transparency: Vivianite is typically translucent to opaque, although some specimens might show slight transparency in thin layers.
Cleavage: Vivianite exhibits good cleavage in one direction, making it prone to splitting along specific planes.
Crystal System: Vivianite belongs to the monoclinic crystal system, characterized by its three unequal axes at angles not all equal to 90 degrees.
Density: Vivianite's density ranges from 2.64 to 2.84 g/cm³, making it slightly heavier than water.
Fracture: Fibrous; breaks into long, thin fibers along cleavage planes.
Solubility: Highly soluble in acids; readily dissolves upon contact.
Magnetism: Non-magnetic; exhibits no magnetic properties.
Fluorescence: Weak orange fluorescence under longwave ultraviolet light; not a defining characteristic.
Pleochroism: Distinct; color changes depending on viewing angle. Appears darker blue-green along one axis and lighter, even greenish, along another.
Refractive Index: 1.569-1.675; a measure of how light bends when passing through the mineral, aiding in identification.
 |
| Crystallised Vivianite from Llallagua, Potosi Department, Bolivia |
Vivianite Uses
Scientific uses:
Environmental indicator: Vivianite's presence in sediments can reveal past environmental conditions, including oxygen levels, pH, and the availability of iron and phosphorus. This information aids in reconstructing paleoclimate and understanding past ecological changes.
Geochemical tracer: Researchers studying the transportation and fate of iron and phosphorus in aquatic environments can utilize vivianite as a natural tracer due to its specific formation conditions and reactivity.
Paleontological tool: Fossilized vivianite alongside fossils of organisms like fish or plants can provide insights into ancient ecosystems and the interactions between organisms and their environment.
Aesthetic uses:
Gemstone: While not as prevalent as other gemstones, vivianite's unique color and crystal formations draw the attention of collectors and jewelry enthusiasts. It can be fashioned into cabochons or faceted stones for rings, pendants, and earrings, though its softness and susceptibility to oxidation necessitate extra care.
Mineral collections: Pristine vivianite specimens, particularly well-developed crystals, are prized additions to mineral collections due to their rarity and visual appeal. Their color variations and crystal forms add to their scientific and aesthetic value.
Decorative objects: Some artisans utilize vivianite in ornamental carvings or sculptures, showcasing its natural beauty and texture. However, such applications require careful selection and treatment due to the mineral's fragility.
Cultural uses:
Symbolic value: In some cultures, vivianite is associated with spiritual growth, emotional well-being, and intuition. It may be used in crystal healing practices, although its effectiveness for such purposes lacks scientific validation.
Historical significance: Archaeological discoveries of vivianite tools and pigments from ancient civilizations offer insights into their material culture and resource utilization.