Is vivianite light sensitive
Vivianite darkens, but its Handbook sheet says oxidation, not light. 7 of 176 sheets record a light response and vivianite is not one. The light claim, weighed.
Is vivianite light sensitive? It darkens, but its Handbook sheet puts that down to oxidation, not light. Seven of the 176 sheets in this site's reference set record a response to light; vivianite, an iron phosphate of hardness 1.5 to 2, is not one. A 1980 study oxidised crystals in air. Light as the trigger is repeated, not verified here.
In short
- The primary sheet names oxidation. The Handbook records vivianite's colour as colorless, very pale green, with oxidation becoming dark blue, dark greenish blue, Indigo-blue, then black, and its streak as white, altering to dark blue, brown. It is the only one of the 176 sheets in this site's reference set whose colour field names oxidation.
- Seven of the 176 sheets record a response to light, and vivianite is not among them. They are realgar, pararealgar, proustite, pyrargyrite, chlorargyrite, baryte and acanthite. Realgar's reads disintegrates on long exposure to light; the two ruby silvers read darkens with exposure to light.
- The 1980 oxidation study used air, not light. McCammon and Burns, in American Mineralogist, call vivianite well known for its vulnerability to atmospheric oxidation. They oxidised it by grinding in air, wrote the reaction with oxygen, and found it faster on fresh surfaces. They did not test light.
- The light account comes from a secondary source. Wikipedia says visible light starts the oxidation within minutes and that no oxygen enters the crystal. Its citation is a 2006 Mindat article, which returned HTTP 403 when fetched for this page. The two accounts disagree on whether oxygen enters; they are set side by side below, not resolved.
- The change is chemical and almost weightless. Vivianite to the metavivianite formula loses two hydrogen atoms: minus 0.40% of the mass, calculated. You cannot weigh the darkening. The colour is the measurement.
| Species | Formula as the sheet prints it | What the sheet says | Cause the sheet names | Hardness |
|---|---|---|---|---|
| Vivianite | Fe3(PO4)2·8H2O | with oxidation becoming dark blue ... then black | Oxidation | 1.5 to 2 |
| Realgar | AsS | Disintegrates on long exposure to light to a powder of pararealgar or arsenolite and orpiment | Light | 1.5 to 2 |
| Pararealgar | AsS | An alteration product of realgar ... typically a result of exposure to light | Light | 1 to 1.5 |
| Proustite | Ag3AsS3 | darkens with exposure to light | Light | 2 to 2.5 |
| Pyrargyrite | Ag3SbS3 | darkens with exposure to light | Light | 2.5 |
| Chlorargyrite | AgCl | turns violet-brown to purple on exposure to light | Light | 2.5 |
| Baryte | BaSO4 | may ... change color on exposure to light | Light | 3 to 3.5 |
| Acanthite | Ag2S | Photosensitive | Light | 2 to 2.5 |
| Marcasite | FeS2 | darkening on exposure, iridescent tarnish | Exposure, not specified | 6 to 6.5 |
| Copper | Cu | Pale rose on fresh surface, quickly darkens to copper-red | Not named | 2.5 to 3 |
Is vivianite light sensitive? What the reference sheets record
Definition first: vivianite darkens because its ferrous iron is oxidised to ferric iron, and the Handbook of Mineralogy sheet records that as oxidation, not as a response to light. Fresh material is colourless to very pale green; the sheet's sequence runs through dark blue and indigo to black, and the streak alters from white to dark blue and brown. The species page, vivianite, covers the colour sequence; this page asks only whether light is the cause.
Method. The 176 sheets in this site's reference set were converted with pdftotext -layout and searched case-insensitively for exposure to light, photosensitive, light-sensitive, sunlight, daylight and affected by light, the last also in its ff-ligature form, which older sheets render as a stray glyph (di®raction); a positive control on that glyph matched 25 sheets. Seven sheets record a response to light: realgar, pararealgar, proustite, pyrargyrite, chlorargyrite, baryte and acanthite. Vivianite is not one. The one daylight hit, scorodite, describes a colour that looks different under different lighting, not a change.
So on the primary reference, vivianite is an oxidising mineral, not a light-sensitive one. That is a statement about what the sheet says, and the next section is about what it does not settle.
Light or air? Two published accounts that disagree
The peer-reviewed account names air. McCammon and Burns, American Mineralogist 65 (1980), describe vivianite as well known for its vulnerability to atmospheric oxidation. They oxidised specimens by grinding them in air for minutes to hours and followed the iron by Mössbauer spectroscopy. The reaction they give turns water ligands on the iron into hydroxyl and consumes oxygen, and it is enhanced as fresh surfaces are exposed. Light was not a variable in the study, and the paper does not mention it.
The light account is in a secondary source. Wikipedia's vivianite article says oxidation is an internal process, that no oxygen or water enters or leaves the crystal, and that it starts when visible light falls on the vivianite, within a few minutes. It cites a 2006 article by Alfredo Petrov on Mindat. That article returned HTTP 403 when fetched on 28 September 2026, so this page has not read it. The two accounts disagree on whether oxygen from outside takes part.
What both agree on: the iron goes from ferrous to ferric, water on the iron becomes hydroxyl, and the colour deepens. Whether light starts it, air feeds it, or both, is not settled by anything verified here. Light may well play a part; this page neither confirms nor dismisses it.
What vivianite darkening is not: realgar, amethyst and tarnish
It is not the realgar case. Realgar's sheet records disintegration on long exposure to light, to a powder of pararealgar or arsenolite and orpiment: a named light reaction that makes other species. The realgar page covers it. Vivianite's sheet names no light reaction.
It is not colour-centre fading. The fading species on which minerals fade in light, amethyst and green fluorite among them, lose colour. Vivianite gains it: its colour comes from charge transfer between neighbouring ferrous and ferric iron, which the 1980 paper describes, so more oxidation means more blue.
It is not tarnish. Eleven sheets in the set record tarnish in their colour field, from bornite, pyrite and silver to hematite: a change at the surface. Both accounts above place vivianite's change in the iron of the crystal itself, not in a film on it.
When the answer changes: fresh, scratched or powdery vivianite
The change is chemical and almost weightless. On the IMA list, metavivianite is Fe2+Fe3+2(PO4)2(OH)2(H2O)6, approved as 1973-049, and santabarbaraite Fe3+3(PO4)2(OH)3·5H2O, 2000-052. Worked with standard atomic weights, vivianite at 501.60 becomes 499.58 at the metavivianite formula, minus 0.40%, and 498.57 at santabarbaraite's, minus 0.60%. A 10.00 g crystal fully converted to the metavivianite formula would weigh 9.96 g. The same arithmetic reproduces the sheet's pure-formula columns exactly: FeO 42.97%, P2O5 28.30%, H2O 28.73%.
Three conditions change what to expect. Fresh, colourless material has the most change ahead of it. Fresh surfaces oxidise faster, according to the 1980 grinding experiments, so a scratch or a new cleavage face at hardness 1.5 to 2 matters. And extensively oxidised vivianite, the same paper says, disintegrates into friable dark blue powder; the sheet records earthy and powdery habits too. Conventional storage precautions are on the species page; they have not been tested here.
Vivianite and bones. The sheet records it replacing organic material in fossil bones, in lake sediments, bog-iron ores and peat bogs. Reports of it on buried human remains appear in secondary sources that could not be opened at source for this page, so it says no more. The conservation pages are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.