Annabergite
Annabergite is hydrated nickel arsenate, Ni3(AsO4)2·8H2O: apple-green, hardness 1.5 to 2.5, in a series with erythrite. Where the nickel-cobalt 50% line falls.
Annabergite is hydrated nickel arsenate, Ni3(AsO4)2(H2O)8 on the September 2026 IMA list: monoclinic, apple-green to pale green, streak pale green to white, hardness 1.5 to 2.5, density 3.07. It forms a series with crimson erythrite, its cobalt analogue. In the Handbook’s Cobalt, Ontario analysis nickel holds 88.6% of the divalent metals.
In short
- The species. The Handbook of Mineralogy sheet gives rare, poorly formed monoclinic crystals to 5 mm, usually fibrous veinlets, crystalline crusts or earthy material; perfect {010} cleavage, sectile, hardness 1.5 to 2.5, density 3.07. Colour apple-green, pale green, pale rose or pale pink, white or gray; streak pale green to white. Vivianite group; it forms a series with erythrite.
- The 50% line. Nickel and Grice 1998, Canadian Mineralogist 36, 913–926 state that in a continuous binary series only the two end-members are species, each running to 50 mol%. Worked on the sheets: the Cobalt, Ontario annabergite has nickel 88.6%, cobalt 8.9% of its divalent metals; the Schneeberg erythrite has cobalt 88.9%, iron 11.1%. Both sit far from the line.
- Documented failure: colour and weight. The annabergite sheet allows pale rose and pale pink; erythrite’s allows pale rose and pink. A 20.00 g piece reads 13.49 g in water as annabergite and 13.46 g as erythrite, 0.03 g apart, at the same hardness. The streak, pale green to white against pale red to pink, is the hand test the sheets offer; the 50% line needs an analysis.
- Documented failure: the new magnesium rows. A script finds 12 IMA rows written ending (AsO4)2(H2O)8. Cabrerite, NiMg2 (2023), gritsenkoite, CoMg2 (2025), and zincocabrerite, ZnMg2 (2026), are magnesium two-thirds by formula, yet each is its own species, not hörnesite, Mg3. Bulk shares alone do not name them.
| Composition | Ni | Co | Mg | Other | Leading metal | IMA row | Density; 20.00 g in water | Colour (sheet) |
|---|---|---|---|---|---|---|---|---|
| Annabergite, ideal Ni3(AsO4)2(H2O)8 | 100% | — | — | — | Ni | G, 1852, Germany | 3.07; 13.49 g | Apple-green, pale green, pale rose or pale pink, white, gray |
| Annabergite, Cobalt, Ontario (sheet analysis 1) | 88.6% | 8.9% | 1.0% | Fe 1.5% | Ni | As above | As above | As above |
| Erythrite, Schneeberg (sheet analysis 1) | — | 88.9% | — | Fe 11.1% | Co | G, 1832, France / Germany ? | 3.06; 13.46 g | Crimson to peach-red, pale rose, or pink |
| Erythrite, ideal Co3(AsO4)2(H2O)8 | — | 100% | — | — | Co | As above | As above | As above |
| Hörnesite, Mg3(AsO4)2(H2O)8 | — | — | 100% | — | Mg | G, 1860, Romania | 2.57–2.73; 12.22–12.67 g | White |
| Cabrerite, NiMg2(AsO4)2(H2O)8 | 33.3% | — | 66.7% | — | Mg by bulk; a separate species | A, 2023-123, USA | n.f. | n.f. |
| Gritsenkoite, CoMg2(AsO4)2(H2O)8 | — | 33.3% | 66.7% | — | Mg by bulk; a separate species | A, 2025-052, Russia | n.f. | n.f. |
| Zincocabrerite, ZnMg2(AsO4)2(H2O)8 | — | — | 66.7% | Zn 33.3% | Mg by bulk; a separate species | A, 2026-013, Morocco | n.f. | n.f. |
| Köttigite, Zn3(AsO4)2(H2O)8 | — | — | — | Zn 100% | Zn | G, 1850, Germany | 3.33; 13.99 g | White, colorless; light carmine, peach-blossom-red (cobaltian) |
What is annabergite? Green nickel arsenate in the vivianite group
Annabergite is the nickel member of the vivianite group, Ni3(AsO4)2·8H2O, a soft green secondary arsenate. The Handbook of Mineralogy annabergite sheet gives monoclinic crystals, rare and typically poorly formed, elongated along [001] and flattened on [010], to 5 mm; usually fibrous veinlets, crystalline crusts or earthy. Cleavage {010} perfect; sectile, with thin {010} laminae flexible; hardness 1.5 to 2.5; density 3.07 measured, 3.146 calculated. It is transparent to translucent, subadamantine and pearly on cleavages.
How it forms. The sheet calls it an uncommon secondary mineral formed by the alteration of Co–Ni-bearing arsenides and sulfides, in the oxidized zone of hydrothermal mineral deposits, associated with erythrite, retgersite, gersdorffite, nickeline, maucherite and nickel-skutterudite. The arsenide side of that story is on skutterudite. The sheet names the mineral for its originally noted occurrence at Annaberg, Germany, and marks no type locality; the IMA list gives Germany, 1852.
What it is made of. Worked from standard atomic weights, ideal Ni3(AsO4)2·8H2O is 29.44% nickel, 25.06% arsenic and 24.10% water by mass; as oxides, NiO 37.47%, As2O5 38.43%, H2O 24.10%, which is what the sheet’s ideal column prints. The Cobalt, Ontario analysis on the sheet has NiO 33.82, CoO 3.40, FeO 0.56, MgO 0.21, As2O5 37.25 and H2O 24.83.
Annabergite or erythrite? Where the 50% line falls
The 50% line: annabergite and erythrite are the nickel and cobalt end-members of one series, and a specimen takes the name of whichever metal is above half. Nickel and Grice 1998, Canadian Mineralogist 36, 913–926 write that in a continuous binary solid-solution series only the two end-members are regarded as species, each applying from its end-member to 50 mol%, and that where more than two atoms share a site, the species is defined by the predominant one. Both the annabergite and the erythrite sheet say the two form a series.
Worked on the sheets. Divide each oxide by its formula weight: the Cobalt, Ontario annabergite gives nickel 2.66, cobalt 0.27, iron 0.05, magnesium 0.03 per three metals, nickel 88.6%. The Schneeberg erythrite gives cobalt 2.67, iron 0.33, cobalt 88.9%. Each analysis sits nearly 40 points inside its own half of the series.
Documented failure: what the eye and the balance cannot do. Colour overlaps at the pink end: the annabergite sheet allows pale rose or pale pink, the erythrite sheet pale rose or pink. Weight fails: 13.49 g in water for 20.00 g as annabergite, 13.46 g as erythrite. Hardness is 1.5 to 2.5 on both. The streak differs on the sheets, pale green to white against pale red to pink; see how to use a streak plate and how to measure specific gravity at home. A pale, zoned crust can carry both sides of the line, and it takes an analysis to place it.
How many minerals share the annabergite formula pattern?
A script over the September 2026 IMA list finds 12 rows whose formula ends (AsO4)2(H2O)8. A field scan and a whole-line token scan agree. Eight carry one divalent metal: annabergite Ni, erythrite Co, hörnesite Mg, köttigite Zn, manganohörnesite Mn2+, parasymplesite and symplesite Fe2+, and babánekite Cu. Four carry two: monteneroite Cu2+Mn2+2 (2020), cabrerite NiMg2 (2023, USA), gritsenkoite CoMg2 (2025, Russia) and zincocabrerite ZnMg2 (2026, Morocco). The phosphate rows with the same pattern include vivianite, Fe2+3(PO4)2(H2O)8, and arupite, the nickel phosphate.
Documented failure: bulk shares cannot name the magnesium rows. Read as a bulk composition, cabrerite is two-thirds magnesium, and so are gritsenkoite and zincocabrerite; hörnesite, Mg3, is all magnesium. All four are separate IMA species. Nickel and Grice say the rule applies site by site, and that in complex structures a designation should be substantiated by a crystal-structure analysis. This page has no structure source for the newer rows, so it states only what the list prints.
The sheets’ series. Erythrite forms two series, with annabergite and with hörnesite; köttigite forms one with parasymplesite. All four of those sheets say vivianite group.
Where is annabergite found?
The annabergite sheet says many localities, but typically in small amounts. Its Distribution field names Annaberg and Schneeberg, Saxony, and Richelsdorf, Hesse, Germany; Dobšiná, Slovakia; Leogang, Austria; the Sierra Cabrera, Almería, and Molvizar, Granada, Spain; the Dolcoath mine, Cornwall, and the Coniston mines, Cumbria; the Leadhills-Wanlockhead district, Scotland; fine examples from the Kamariza, Plaka and Verzekos mines and along the road to Laurium, Greece (Lavrion); the Bou Azzer district, Morocco; the Talmessi mine, Anarak, Iran; and Cobalt, Ontario, among others.
Names and limits. The IMA list has one line containing annabergite and none containing nickel bloom; no source fetched for this page gives an alternative name, so none is offered. USGS OFR 99-529 Table 1 has no annabergite row. Ideal annabergite is 25.06% arsenic; see toxic minerals in a collection, which is not advice. The rest is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.