Ludlamite vs vivianite
Two iron phosphate species, same mines. Ludlamite crystals are green, hardness 3.5; vivianite is soft, 1.5 to 2, and oxidises blue. A fingernail decides.
Ludlamite or vivianite? Both are hydrated iron phosphates, monoclinic, from many of the same mines, but they separate at home. Ludlamite is apple-green, hardness 3.5, density 3.12 to 3.19. Vivianite is colourless to pale green turning blue to black, hardness 1.5 to 2, flexible, density 2.68. A fingernail marks vivianite and not ludlamite.
In short
- Same family, different water. The Handbook of Mineralogy prints ludlamite with four waters and vivianite with eight; the September 2026 IMA list writes them Fe2+3(PO4)2(H2O)4 and Fe2+3(PO4)2(H2O)8. Worked on standard atomic weights, that is 16.78% water by mass against 28.73%, and both sheets print the same figures in their ideal columns.
- The fingernail rule: a fingernail, about 2.5, marks vivianite (1.5 to 2) and does not mark ludlamite (3.5). Vivianite is also recorded as flexible and sectile; ludlamite's sheet records no tenacity. Test on the base, never on a crystal face.
- Blue points to vivianite. Vivianite's sheet records colourless to very pale green, becoming dark blue, indigo-blue, then black with oxidation, and a white streak that alters to dark blue or brown. Ludlamite's sheet records apple-green to bright green and a pale greenish white streak, and no blue.
- The scale gives the same verdict. A 20.00 g piece reads 13.59 to 13.73 g in water as ludlamite and 12.54 g as vivianite, a gap of 1.05 g, calculated from the measured densities.
- A label does not decide. Seven places are named on both sheets' Distribution fields, and each sheet lists the other mineral among its associates. Metavivianite, formed from oxidising vivianite, is leek-green to brown, so a green crystal needs a second check.
| Criterion | Ludlamite | Vivianite | Metavivianite | Does it choose? |
|---|---|---|---|---|
| Formula, Handbook | (Fe2+,Mg,Mn2+)3(PO4)2·4H2O | Fe2+3(PO4)2·8H2O | Fe2+3-xFe3+x(PO4)2(OH)x·(8-x)H2O | Only by analysis |
| Formula, IMA list (Sept 2026) | Fe2+3(PO4)2(H2O)4; G, 1885 | Fe2+3(PO4)2(H2O)8; G, 1817 | Fe2+Fe3+2(PO4)2(OH)2(H2O)6; A, 1973-049 | - |
| Water by mass, ideal | 16.78% | 28.73% | Not calculated (x varies) | Only by analysis |
| Crystal system | Monoclinic | Monoclinic | Triclinic | No, by eye |
| Crystals | Usually tabular on {001}, to 9 cm; granular, massive | Prismatic, to 1.3 m; stellate groups, earthy, powdery | Prismatic, to 9 cm; typically pseudomorphous after vivianite | Suggestive only |
| Colour | Apple-green to bright green | Colourless, very pale green; with oxidation dark blue, indigo-blue, then black | Leek-green, khaki-green, brown | Yes, if blue or blue-black |
| Streak | Pale greenish white | White, altering to dark blue, brown | Not recorded | Partly: vivianite's alters to dark blue or brown |
| Hardness | 3.5 | 1.5–2 | Not determined | Yes: the fingernail rule |
| Tenacity | Not recorded | Flexible, sectile | Not recorded | Yes: thin vivianite blades bend |
| Cleavage | {001} perfect; {100} indistinct | Perfect on {010} | Perfect on {110} | Not by eye |
| Density, measured | 3.12–3.19 | 2.68 | Not determined (2.69 calculated) | Yes, against vivianite |
| 20.00 g piece in water | 13.59–13.73 g | 12.54 g | 12.57 g, from calculated density | Ludlamite against the others: yes. Vivianite against metavivianite: no |
| Refractive index, alpha | 1.650–1.653 | 1.579–1.616 | 1.579 | Only on a refractometer |
Ludlamite vs vivianite: what each sheet says they are
Ludlamite and vivianite are both hydrated ferrous iron phosphates, and they differ first in how much water they hold. The Handbook of Mineralogy sheet for ludlamite prints (Fe2+,Mg,Mn2+)3(PO4)2·4H2O; the Handbook of Mineralogy sheet for vivianite prints Fe2+3(PO4)2·8H2O, in the vivianite group. The IMA-CNMNC list of minerals gives Fe2+3(PO4)2(H2O)4 and Fe2+3(PO4)2(H2O)8, both grandfathered, ludlamite from 1885 and vivianite from 1817, and gives the United Kingdom as the country of first description for each.
Worked on standard atomic weights (Fe 55.845, P 30.974, O 15.999, H 1.008), ludlamite's ideal formula weighs 429.535 g/mol and is 16.78% water; vivianite's weighs 501.595 g/mol and is 28.73% water. Both sheets print exactly those water figures in their ideal-composition columns. The extra water is why vivianite is lighter: 2.68 measured against ludlamite's 3.12 to 3.19.
Names, not places. Ludlamite honours Henry Ludlam (1824–1880), an English collector in London, and its type material is at the Natural History Museum, London. Vivianite honours John Henry Vivian (1785–1855) of Truro, who discovered the species. The ludlamite sheet marks no type locality, and this page names none. Both species have their own pages: ludlamite and vivianite.
How do I tell ludlamite from vivianite? The fingernail rule
The fingernail rule: a fingernail marks vivianite and does not mark ludlamite. The sheets give vivianite hardness 1.5 to 2 and ludlamite 3.5; a fingernail sits at about 2.5 on this site's hardness testing guide. That is half a point above vivianite's top figure and a full point below ludlamite. Vivianite's sheet adds tenacity flexible and sectile, so a thin blade bends rather than snaps; ludlamite's records no tenacity. Test on the base or matrix, never on a display face.
Colour and streak point the same way. Vivianite is colourless to very pale green when fresh and, on its sheet, becomes dark blue, dark greenish blue, indigo-blue, then black with oxidation; its white streak alters to dark blue or brown. Ludlamite is apple-green to bright green with a pale greenish white streak, and its sheet records no blue. A blue or blue-black crystal is not ludlamite on this evidence. Why vivianite darkens, and what is and is not known about light, is set out on is vivianite light sensitive; it is not repeated here.
The scale is the check that leaves no mark. Worked as weight in water equals mass times one minus one over density, a 20.00 g piece reads 13.59 to 13.73 g as ludlamite and 12.54 g as vivianite. The method and the scale resolution it needs are on how to measure specific gravity at home.
Is green vivianite ludlamite? The metavivianite trap
A green crystal from a vivianite locality may be ludlamite, fresh vivianite or metavivianite, and only one of them is reliably hard. The Handbook of Mineralogy sheet for metavivianite records leek-green, khaki-green and brown crystals to 9 cm, typically pseudomorphous after vivianite, and calls it a secondary mineral typically formed from oxidizing vivianite. Its hardness and measured density are not determined; its calculated density, 2.69, gives 12.57 g in water for a 20.00 g piece, indistinguishable from vivianite's 12.54 g.
A documented negative: the scale separates ludlamite from both, but not vivianite from metavivianite. Telling those two apart is a structural question, monoclinic against triclinic, and in our judgement a laboratory one. For a green crystal, the order is hardness on a hidden spot first, then the scale. A green crystal that resists a fingernail and reads above 13.5 g per 20 g fits ludlamite.
Who each answer is wrong for. Ludlamite is the wrong answer for anything blue, blue-black or bendable. Vivianite is the wrong answer for a bright green crystal that a fingernail will not mark. Neither suits a pale, earthy crust you cannot test without destroying it; the honest label there is iron phosphate, untested. The identification pages are indexed at the collecting guides.
Why ludlamite and vivianite share localities
Seven places are named on both sheets' Distribution fields: Hagendorf, Bavaria; the Stari Trg mine, Trepča; the Blackbird mine, Idaho; Santa Eulalia, Chihuahua; the Énio pegmatite mine near Galiléia, Minas Gerais; Morococala, Bolivia; and the Ashio mine, Japan. Counted by reading the two fields side by side. Cornwall makes it eight at parish level: ludlamite from Wheal Jane, Kea, and vivianite from other mines in St. Just and Kea.
They are recorded together, too. Ludlamite's Association field lists vivianite at the Palermo #1 mine, New Hampshire, with fairfieldite, siderite and whitlockite; vivianite's lists ludlamite with metavivianite, pyrite and pyrrhotite. Ludlamite occurs in complex granite pegmatites as an alteration product of earlier phosphates under reducing conditions; vivianite in oxidized ore zones, pegmatites, fossil bone and bog-iron ores. The metavivianite sheet names Wheal Jane as well. So a Cornish, Bolivian or Hagendorf label narrows nothing; see Cornwall and Minas Gerais.
Test each crystal, not the specimen. On a mixed piece, the green tabular crystal and the blue prism beside it can be different species. Nothing on this site is offered for sale; the wanted list is the only commercial route.