Vivianite

Vivianite is a soft mineral, with Mohs hardness only ​1 ⁄2 to 2, and specific gravity 2.7. It splits easily, with perfect cleavage perpendicular to the b crystal axis, due to the sheet-like structure of the mineral. It is sectile, with a fibrous fracture, and thin laminae parallel to the cleavage plane are flexible. It is easily soluble in acids. It has a melting point of 1,114 °C (2,037 °F), it darkens in color in H2O2 and is not radioactive.

The mineral may occur as crystals, or as masses or concretions. The crystals are usually prismatic parallel to the c crystal axis, and flattened perpendicular to the b axis. Equant crystals are rarer. They may also occur as stellate (star-shaped) groups, or encrustations with a bladed or fibrous structure. Unaltered specimens are colorless to very pale green, but they oxidize on exposure to light (and possibly also in situ) to blue, then darker green, brown, purple and purplish black. The streak is white, altering to dark blue or brown. Crystals are transparent to translucent with a vitreous luster, pearly on the cleavage surface, or dull and earthy.

In pure end member vivianite all the iron is divalent, Fe, but there are two distinct sites in the structure that these ions can occupy. In the first site the Fe is surrounded by four water molecules and two oxygens, making an octahedral group. In the second site the Fe is surrounded by two water molecules and four oxygens, again making an octahedral group. The oxygens are part of the phosphate groups (PO4), that are tetrahedral. The vivianite structure has chains of these octahedra and tetrahedra that form sheets perpendicular to the a crystal axis. The sheets are held together by weak bonds, and that accounts for the perfect cleavage between them. The crystals are monoclinic, class 2/m, space group C 2/m, with two formula units per unit cell (Z = 2). The approximate values of the unit cell parameters are a = 10.1 Å, b = 13.4 Å, c = 4.7 Å and β = 104.3°, with slightly different values given by different sources: a = 10.086 Å, b = 13.441 Å, c = 4.703 Å, β = 104.27° a = 10.06 Å, b = 13.41 Å, c = 4.696 Å, β = 104.3° a = 10.034–10.086 Å, b= 13.434–13.441 Å, c= 4.687–4.714 Å, β = 102.65–104.27° a = 10.024(6) Å, b = 13.436(3) Å, c = 4.693(4) Å, β = 102.30(5)°

Vivianite is very popular among collectors as raw specimens and as gemstones. However, there are no known industrial or household uses for this mineral. Vivianite was historically once used as a pigment in oil paints, though it is rarely used in that context in modern times.

Brazil. Cigana Mine, Galileia, Minas Gerais, with muscovite and pyrite. Typically wedge-shaped crystals of vivianite to 11 cm across, of medium lustre, smoke-blue color and good transparency on matrix of sharp silvery muscovite plates, some with druses of pyrite microcrystals.

Brazil: Llallagua, Potosi: Crystals to 10 cm at the Siglio XX mine. Transparent bottle green crystals to 10 cm from the San Jose/San Firmin vein. In general the vivianite occurs as prismatic crystals on a matrix of botryoidal goethite derived from the alteration of pyrite and marcasite. Specimens found in 2000 were associated with childrenite, cronstedtite, pyrrhotite, frankeite and pink massive sphalerite.

Cameroon: The world's largest vivianite crystals (more than a meter long) from mud.

Canada: In bog iron at Côte St Charles, Vaudreuil-Soulanges, Montérégie, Québec.

Germany: In the limonite ores in Amberg-Auerbach and in the pegmatites of Hagendorf, Bavaria.

Japan: At Nagasawa, Iwama-machi, Ibaraki Prefecture, vivianite was found along fractures in rocks rich in graphite, pyrite and pyrrhotite. The vivianite is intimately associated with pyrite and occurs as very thin tabular crystals, up to 10 cm in length.

Kosovo. Trepča Mines, Stari Trg. Thick prismatic crystals up to 10 cm long and 2 cm thick, relatively stable. Deep green in color and transparent, commonly resting on pyrrhotite or pyrite, and in some cases on quartz or carbonates.

Mexico: In blue-green gem quality crystals to 8 cm at the San Antonio Mine, Santa Eulalia, Chihuahua.

Russia: In sedimentary iron ores and in fossil shells in the Kerch and Taman peninsula on the Black Sea.

Spain: At the Brunita mine, Cartagena, Murcia, vivianite was found as deep green crystals, up to 8 cm

USA: In diatomite in a tertiary lake bed near Burey, Shasta County, California.

USA: In green sand at Middletown, New Castle County, Delaware.

USA: Blackbird Mine, Lemhi County, Idaho. Crystals in shades of pink, green, greyish blue, purple and purplish black, as well as colorless. The unique deep purple color of some Blackbird mine specimens is characteristic of the locality. Some single crystals have both purple and green zones. Vivianite crystals from the Blackbird Mine are usually elongated and blade-like. They occur as singles and groups on dark altered schist and on white quartz. Associated minerals include ludlamite, quartz and siderite.

USA: Abundant in the pegmatites of Newry, Maine.

New Zealand: Small amounts of vivianite are present within the sediments of Lake Kohangapiripiri.

Vivianite is a secondary mineral found in a number of geologic environments: The oxidation zone of metal ore deposits, in granite pegmatites containing phosphate minerals, in clays and glauconitic sediments, and in recent alluvial deposits replacing organic material such as peat, lignite, bog iron ores and forest soils (All). Bones and teeth buried in peat bogs are sometimes replaced by vivianite. Some authors say that it is particularly associated with gossan, but this is disputed by Petrov.

Associated minerals include metavivianite, ludlamite, pyrite, siderite and pyrrhotite. Hydrothermal veins produce the best crystal specimens with the classic gemmy green color.

The type locality is Wheal Kind (Wheal Kine), West Wheal Kitty group, St Agnes, St Agnes District, Cornwall, England.

It was named by Abraham Gottlob Werner in 1817, the year of his death, after either John Henry Vivian (1785–1855), a Welsh-Cornish politician, mine owner and mineralogist living in Truro, Cornwall, England, or after Jeffrey G. Vivian, an English mineralogist. Vivianite was discovered at Wheal Kind, in St Agnes, Cornwall.

Vivianite is believed to be a restorative stone that will help to remove negative energy from your emotional, physical and spiritual body and replace it with positive healing energy. It is said that just holding the crystal in the hand can revitalize the individual. It is often used to alleviate stress and help boost a more positive outlook, allowing an individual to move forward in life.