Vivianite
Vivianite is a hydrated iron phosphate, hardness 1.5 to 2, colourless when fresh and darkening to indigo and black. Cornish type locality and Bolivian crystals.
Vivianite is a hydrated iron phosphate, hardness 1.5 to 2, described in 1817 and named for John Henry Vivian (1785-1855), who found it in Cornwall. Fresh material is colourless to pale green; oxidation turns it blue, then indigo, then black. Prismatic crystals reach 1.3 m.
In short
- The colour is the damage. The deep indigo that makes vivianite famous is an oxidation product. Genuinely fresh vivianite is nearly colourless, and every specimen you see is already partway through the change.
- It is very soft and it bends. Hardness 1.5 to 2, perfect cleavage on {010}, and flexible, sectile crystals — you can cut it with a knife and it will deform rather than snap.
- The type locality is British: Cornwall, at St Agnes, with other material from mines in St Just and Kea. Almost nobody associates the species with Cornwall, and the label does.
- The best crystallised specimens are Bolivian, from Llallagua and the other tin districts, with huge crystals also from Anloua in Cameroon.
- It forms in the oxidised zone of metallic ore deposits and in granite pegmatites, but also in bog iron ores, peat, lake sediments and replacing organic material in fossil bone.
| State | Colour | What has happened | What to do |
|---|---|---|---|
| Fresh, unexposed | Colourless to very pale green | Iron still in the ferrous state | Seal it dark immediately. This state does not survive display |
| Early oxidation | Blue to dark greenish blue | Partial oxidation to ferric iron | The state most collectors want. Stabilise by storing dark and dry |
| Advanced | Indigo to dark blue, strongly pleochroic | Further oxidation through the crystal | Still a fine specimen. Handle minimally |
| Terminal | Brown, purplish black, black; streak brown | Oxidation essentially complete; crystals often crumbling | Not recoverable. Photograph and keep the label |
A Cornish type locality nobody expects
Vivianite is named for John Henry Vivian, 1785 to 1855, the Welsh-Cornish mineralogist of Truro who discovered the species, and it was described in 1817. The Handbook of Mineralogy gives the English occurrences as St Agnes and other mines in St Just and Kea, Cornwall, with the type material from the St Agnes district.
This is worth knowing for a specific practical reason: it is one of the small number of species with a British type locality that collectors do not associate with Britain at all. Cornish vivianite is scarce, it is old — the mines were finished long ago, as our Cornwall page sets out — and it is not what anyone means when they say vivianite. That combination is exactly the one where a well-documented old label carries disproportionate weight, and where an under-described piece in a mixed lot occasionally turns out to be significant. Our notes on old labels cover what makes such a label checkable.
Do not, however, expect Cornish material to look like the Bolivian crystals in photographs. It does not. British vivianite is generally small, often earthy or crusty, and its interest is historical rather than aesthetic.
The colour, and why it is a clock
Vivianite is one of the clearest examples in mineralogy of a species whose famous appearance is a state of decay. Freshly exposed material is transparent and colourless to very pale green. On exposure the ferrous iron oxidises, and the crystal runs through dark blue, dark greenish blue and indigo, then to brown, purplish black and finally black. The streak follows: white at first, altering to dark blue and then brown.
Two consequences for a collector. First, a colourless vivianite is a very recent one, and it will not stay colourless. Second, the process does not stop where you would like it to. The rich indigo that people buy is a waypoint, not an end state, and the specimen continues to darken in a cabinet, slowly, indefinitely.
What you can do is slow it. Store the specimen sealed and dry, keep it dark, and handle it as little as possible — the same regime as for the genuinely light-sensitive species on our page about minerals that fade in light, applied here to an oxidation rather than a photochemical reaction. What you cannot do is reverse it. There is no treatment that puts a black vivianite back to blue, and any specimen offered as unusually bright should prompt the same questions as any other suspiciously good colour.
The pleochroism is worth seeing while you have the chance: in transmitted light the crystal is deep blue in one direction and pale yellowish or bluish green in the others, which is unusually strong for a common mineral and is diagnostic.
Softness, cleavage and handling
At hardness 1.5 to 2, vivianite is softer than a fingernail is hard in the wrong direction, and it has perfect cleavage on {010}. The tenacity is the unusual part: it is flexible and sectile, so a thin cleavage plate bends rather than shattering and a blade cuts it. That makes it one of the very few minerals that a careless thumb can permanently deform rather than merely chip.
Handling rules that follow, and they are stricter than for most species:
- Support it under the matrix. Never grip a crystal.
- Store it in its own rigid box, with nothing else in the box. Anything harder — which is nearly everything — will mark it.
- Do not clean it. Water, ultrasonic baths and brushes are all worse than the dust.
- If it must be shipped, it is in the softest class on our page about packing and shipping specimens: tissue and cut foam, nothing touching the crystals, double boxed.
Where the great crystals come from
The species is widespread — it turns up in bog iron ore, in peat, in lake sediment, and famously replacing organic material in fossil bone, which is why palaeontologists know it as well as mineralogists do. Well-crystallised material is another matter.
Bolivia is the standard, with exceptional examples from Llallagua, Poopó, Avicaya, Tazna, Monserrat, Morococala and Tatasi — the tin and silver districts of the Altiplano. Huge crystals come from Anloua, near Ngaoundéré in Cameroon; the largest recorded prismatic crystals of the species reach 1.3 m. Other significant localities are Hagendorf in Bavaria, the Stari Trg mine at Trepča in Serbia — which is also a fine pyrrhotite locality — the Taman Peninsula in Russia, Kerch in Crimea, the Énio pegmatite near Galiléia in Minas Gerais, Santa Eulalia in Chihuahua, and several American occurrences including the Blackbird mine in Idaho and the Foote mine in North Carolina.
When buying, the questions that matter are about storage rather than about the mineral: how long has it been out of the ground, how has it been kept, and has anything been done to the colour. A seller who can answer the first two has usually taken care of the third. If a good crystallised vivianite with a real locality is what you want, put it on the wanted list — we hold no stock, and on a species this fragile the value in having somebody look first is unusually high.