Ilvaite
Ilvaite, CaFe3+Fe2+2O(Si2O7)(OH): iron-black prismatic silicate, hardness 5.5–6, density 3.99–4.05, 40.98% iron, named for Elba, fine at Dalnegorsk. Sheet data.
Ilvaite is a calcium iron silicate, CaFe3+Fe2+2O(Si2O7)(OH) on the September 2026 IMA list: iron-black, submetallic, in striated prisms to 25 cm, hardness 5.5 to 6, density 3.99 to 4.05. Worked from the formula it is 40.98% iron, two parts ferrous to one ferric. It is named for Elba (Latin Ilva), where it was first found.
In short
- The species. The September 2026 IMA-CNMNC Master List lists ilvaite as CaFe3+Fe2+2O(Si2O7)(OH), status G, 1811, Italy. The Handbook of Mineralogy sheet writes CaFe2+2Fe3+OSi2O7(OH): orthorhombic or monoclinic, prismatic crystals striated parallel to {001}, to 25 cm, cleavage distinct on {001} and {010}, hardness 5.5 to 6, density 3.99 to 4.05, iron-black with a black streak inclining to green or brown. A 20.00 g piece reads 14.99 to 15.06 g in water.
- The two-to-one iron check. Worked on standard atomic weights, the formula is 40.98% iron: 27.32% from two Fe2+ and 13.66% from one Fe3+. The sheet’s ideal column (SiO2 29.40, Fe2O3 19.53, FeO 35.15, CaO 13.72, H2O 2.20) reproduces exactly. Its Ilímaussaq, Greenland, analysis recasts per 2 Si to Fe2+ 1.91, Mn 0.11, Fe3+ 1.04 and Ca 1.00.
- Documented failure: the ratio and the cell. Iron alone gives Fe2+ to Fe3+ of 1.83, not 2; only by counting manganese with the ferrous iron, an assumption the sheet does not state, does it reach 1.94. And both printed cells give 4.050 and 4.051, not the printed calculated 4.064; they sit at the top of the measured 3.99 to 4.05.
- Elba and Dal’negorsk. The sheet names the mineral from Ilva, Latin for Elba, “on which it was first found”, and lists Rio Marina and Capo Calamita there. It records very large crystals from Seriphos, Greece, fine crystals at Dal’negorsk, Russia, and splendid crystals from the Laxey mine, Idaho. It marks no type locality; the IMA list gives Italy.
- Its black neighbours. Magnetite, an ilvaite associate on the sheet, is 72.36% iron by formula; hedenbergite, another, 22.51%. On babingtonite ilvaite is one of eight dark silicates set side by side; it is the heaviest of them in water.
| Source | SiO2 | Fe2O3 | FeO | MnO | CaO | H2O | Fe3+ per 2 Si | Fe2+ (+ Mn) per 2 Si | Reading |
|---|---|---|---|---|---|---|---|---|---|
| Formula, worked | 29.40 | 19.53 | 35.15 | — | 13.72 | 2.20 | 1 | 2 | 40.98% Fe: 27.32 ferrous + 13.66 ferric |
| Sheet ideal column (2) | 29.40 | 19.53 | 35.15 | — | 13.72 | 2.20 | 1 | 2 | Reproduces exactly |
| Ilímaussaq intrusion, Greenland (1); total 100.68 | 29.30 | 20.30 | 33.50 | 1.97 | 13.71 | 1.90 | 1.043 | 1.912 (+ 0.114 Mn = 2.026) | Fe2+:Fe3+ 1.83; with Mn 1.94; Ca 1.003 |
| Pbnm cell, a 8.800, b 13.019, c 5.852 Å | — | — | — | — | — | — | — | — | V 670.45 ų: 4.050 |
| P21/a cell, a 13.0103, b 8.8039, c 5.8517 Å, β 90.209° | — | — | — | — | — | — | — | — | V 670.26 ų: 4.051 |
| Printed densities | — | — | — | — | — | — | — | — | 4.064 calc.; 3.99–4.05 meas.: 14.99–15.06 g in water for 20.00 g |
What is ilvaite? A calcium iron silicate
Ilvaite is CaFe3+Fe2+2O(Si2O7)(OH) on the September 2026 IMA list, status G, grandfathered, 1811, with Italy as the country of first description. The first reference is the Vollständiges Handbuch der Oryktognosie, Erster Theil (Halle, 1811), 356, and the second Physics and Chemistry of Minerals 32 (2005), 388. The Handbook of Mineralogy ilvaite sheet writes CaFe2+2Fe3+OSi2O7(OH): the same atoms, with the ferrous iron listed first.
What the sheet records. Orthorhombic or monoclinic, point group 2/m 2/m 2/m or 2/m; “Orthorhombic and monoclinic forms are known.” Crystals are prismatic, striated parallel to {001}, to 25 cm; also columnar, radiating or compact massive. Cleavage distinct on {001} and {010}; fracture uneven; brittle; hardness 5.5 to 6. Opaque, translucent in fine fragments; iron-black or dark greyish black; streak black, inclining to green or brown; lustre submetallic. Biaxial (+), α 1.727, β 1.870, γ 1.883, 2V 20° to 30°, with intense pleochroism in thin section (dark green, yellow-brown to dark brown, dark brown) and very strong anisotropism in reflected light.
Where it forms. The Occurrence field: in contact metasomatic rocks and iron deposits, and in metamorphosed limestones and dolostones with other calc-silicate minerals. Its associates are quartz, magnetite, hedenbergite, sphalerite and fluorite.
How much iron is in ilvaite? The two-to-one iron check
The formula, worked. On standard atomic weights CaFe3+Fe2+2O(Si2O7)(OH) has a formula mass of 408.78. Iron is three of its atoms and 40.98% of its mass: 27.32% as the two Fe2+ and 13.66% as the one Fe3+. Calcium is 9.80%, silicon 13.74%, oxygen 35.22% and hydrogen 0.25%. Expressed as oxides that is SiO2 29.40, Fe2O3 19.53, FeO 35.15, CaO 13.72 and H2O 2.20, which is exactly the sheet’s ideal column (2).
The analysis, recast. The sheet’s one analysis, from the Ilímaussaq intrusion, Greenland, totals 100.68 with SiO2 29.30, Fe2O3 20.30, FeO 33.50, MnO 1.97, CaO 13.71 and H2O 1.90. Per 2 silicon it gives 1.043 Fe3+, 1.912 Fe2+, 0.114 Mn and 1.003 Ca, and 40.24% iron by weight. Calcium and ferric iron sit on the formula.
Documented failure: two to one is not quite two to one. Iron alone gives Fe2+ to Fe3+ of 1.83. Only if the manganese is counted with the ferrous iron, which the sheet does not say, does the ratio reach 1.94. A second failure is in the cells: the orthorhombic Pbnm cell gives 4.050 and the monoclinic P21/a cell 4.051, so the two settings agree with each other to within 0.03% of volume, but neither gives the printed calculated density of 4.064. Both land at the top of the measured range, 3.99 to 4.05.
How to recognise ilvaite in the hand
Habit and streak. Long black prisms striated parallel to {001}, to 25 cm, with a submetallic lustre and a black streak that may lean green or brown, on the method at how to use a streak plate.
Weight. At 3.99 to 4.05, a 20.00 g piece reads 14.99 to 15.06 g in water, on the method at how to measure specific gravity at home. Babingtonite’s page sets ilvaite beside augite, epidote, hedenbergite, aegirine and andradite with the same figures, and that comparison is not repeated here. Hardness 5.5 to 6 does not separate it from the dark pyroxenes.
Magnetite, its associate. Magnetite, Fe3O4, is 72.36% iron by formula against ilvaite’s 40.98%. This page states no magnetic behaviour for ilvaite, because its sheet prints none; the general question is on which minerals are magnetic.
Where is ilvaite found? Elba, Seriphos and Dal’negorsk
Distribution, as printed. “Many localities, even for fine material.” From Elba, at Rio Marina and Capo Calamita; on Mt. Mulatto, near Predazzo, Trentino-Alto Adige, Italy. Very large crystals from Seriphos, Cyclades Islands, Greece. In Germany, at St. Andreasberg, Harz Mountains; near Herborn, Hesse; and Schneeberg, Saxony. At Fossum, near Skeen, Norway; Thyrill, Iceland; the Kangerdluarssuk Plateau in the Ilímaussaq intrusion, southern Greenland; the Kamioka mine, Gifu Prefecture, and the Obira mine, Oita Prefecture, Japan. Fine crystals at Dal’negorsk, Primorskiy Kray, Russia. In the USA, splendid crystals from the Laxey mine, South Mountain, Owyhee Co., Idaho; Middlemarch Pass, Dragoon Mountains, Arizona; and Copper Mountain, Prince of Wales Island, Alaska.
The name and Elba. The sheet derives the name “From the Latin name, Ilva, for the Island of Elba, on which it was first found.” It marks no type locality, and the IMA list gives the country only, Italy; the distinction is explained at what is a type locality.
Elsewhere on this site. The Dal’negorsk skarn suite is covered on its locality page. More silicates are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.