Babingtonite
Babingtonite, Ca2Fe2+Fe3+Si5O14(OH): triclinic, dark greenish black, hardness 5.5 to 6, density 3.34 to 3.37, three cleavages. Augite, epidote match its weight.
Babingtonite is a calcium iron silicate, Ca2Fe2+Fe3+Si5O14(OH) on the IMA list (G, 1824, Norway): triclinic, in stubby, striated, dark greenish black prisms to 3 cm, hardness 5.5 to 6, density 3.34 to 3.37, cleavage perfect on {001} and good on {010} and {100}. A 20.00 g piece reads 14.01 to 14.07 g in water.
In short
- The species. The Handbook of Mineralogy sheet gives Ca2(Fe2+,Mn)Fe3+Si5O14(OH), triclinic, in stubby, prismatic, striated crystals to 3 cm, also platy; cleavage perfect on {001}, good on {010} and {100}; hardness 5.5 to 6; density 3.34 to 3.37; dark greenish black, vitreous, opaque to faintly translucent. The September 2026 IMA-CNMNC Master List writes Ca2Fe2+Fe3+Si5O14(OH), status G, 1824, Norway.
- The black-prism check. Against 7 sheets for dark, prismatic or associated minerals, hardness 5.5 to 6 together with an in-water weight of 14.01 to 14.07 g for 20.00 g leaves 2: augite (5.5 to 6; 13.73 to 14.38 g) and epidote (6 to 7; 14.08 to 14.27 g, 0.02 g away). Cleavage parts them: babingtonite prints three cleavage forms, augite good {110} at about 87° with partings, epidote perfect {001} and imperfect {100}.
- The iron split, worked. The ideal formula holds one Fe2+ and one Fe3+: 13.93% Fe2O3 and 12.53% FeO, as the sheet’s ideal column prints. The Arendal, Norway, analysis works out at 61% of its iron ferric, Holyoke, Massachusetts, at 56%; manganese takes 17% and 8% of the divalent site, iron 68% and 82%.
- The Si5O14(OH) family. A script finds 10 rows on the IMA list written with Si5O14(OH): babingtonite, manganbabingtonite and scandiobabingtonite, and seven Mn2+ rows, among them nambulite, marsturite and santaclaraite. The sheet says babingtonite forms a series with manganbabingtonite, Ca2Mn2+Fe3+Si5O14(OH), whose own sheet prints hardness 6.5 to 7 and density 3.452.
- Massachusetts and elsewhere. The sheet names exceptional crystals from Lane’s quarry, Westfield, the Cheapside and Deerfield quarries, East Deerfield, and Winchester Highlands, Uxbridge, in Massachusetts; the Brastad mine near Arendal, Norway; Baveno, Italy; and the Khandivali quarry near Bombay, India. No fetched source gives it a use, and this page claims none.
| Name | Formula (IMA) | System (sheet) | Hardness | 20.00 g piece in water | Cleavage (sheet) | Colour (sheet, dark entries) | Matches babingtonite on |
|---|---|---|---|---|---|---|---|
| Babingtonite | Ca2Fe2+Fe3+Si5O14(OH) | Triclinic | 5.5–6 | 14.01–14.07 g | Perfect {001}; good {010} and {100} | Dark greenish black | — |
| Augite | (Ca,Mg,Fe)2Si2O6 | Monoclinic | 5.5–6 | 13.73–14.38 g | Good {110}, about 87°; partings {100}, {010} | Black, brown, greenish | Both |
| Epidote | Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH) | Monoclinic | 6–7 | 14.08–14.27 g | Perfect {001}; imperfect {100} | Greenish black, among others | Both (0.02 g) |
| Hedenbergite | CaFe2+Si2O6 | Monoclinic | 5.5–6.5 | 14.38 g | Good {110}, about 87°; partings {100}, {010} | Black, dark green | Hardness only |
| Aegirine | NaFe3+Si2O6 | Monoclinic | 6 | 14.29–14.44 g | Good {110}, about 87°; parting {100} | Dark green to greenish black, black | Hardness only |
| Ilvaite | CaFe3+Fe2+2O(Si2O7)(OH) | Orthorhombic or monoclinic | 5.5–6 | 14.99–15.06 g | Distinct {001} and {010} | Iron-black or dark grayish black | Hardness only |
| Manganbabingtonite | Ca2Mn2+Fe3+Si5O14(OH) | Triclinic | 6.5–7 | 14.21 g | Perfect {001}; less perfect {010}; poor {100} | Dark greenish black | Neither |
| Andradite (garnet) | Ca3Fe3+2(SiO4)3 | Cubic | 6.5–7 | 14.74–14.87 g | None printed | Grayish black, black, among others | Neither |
What is babingtonite? A triclinic calcium iron silicate
Babingtonite is Ca2Fe2+Fe3+Si5O14(OH), a dark greenish black triclinic silicate that carries iron in both valence states. The Handbook of Mineralogy babingtonite sheet gives point group 1̄ and space group P1̄, a 7.50, b 12.18, c 6.68 Å, Z 2: stubby, prismatic, striated crystals to 3 cm, also platy and as subparallel aggregates. Cleavage perfect on {001}, good on {010} and {100}; fracture uneven; brittle; hardness 5.5 to 6; measured density 3.34 to 3.37 against a calculated 3.26.
Colour and optics. Dark greenish black, opaque to faintly translucent, vitreous; the sheet prints no streak. Biaxial (−), α 1.700, β 1.710, γ 1.725, 2V 50°, read from the rendered sheet; the birefringence, worked, is 0.025. Pleochroism X deep green, Y lilac-brown, Z pale to deep brown, with strong dispersion, r > v.
What the lists record. The September 2026 IMA list writes Ca2Fe2+Fe3+Si5O14(OH), status G, 1824, Norway, first reference Annals of Philosophy 7 (1824), 275. The Handbook writes Ca2(Fe2+,Mn)Fe3+Si5O14(OH), allowing manganese beside the ferrous iron, and names the mineral for Dr. William Babington (1756–1833), Irish physician and mineralogist. It occurs in veins cutting granite pegmatite and diorite, in cavities and vugs in mafic volcanic rocks and gneisses, and in skarns, with prehnite, calcite, epidote, albite, orthoclase, garnet, quartz, “hornblende” and zeolites.
Babingtonite, augite or epidote? The black-prism check
Hardness and weight together leave two of seven dark look-alikes; cleavage parts the last two. Method: babingtonite was set against the cached sheets for augite, hedenbergite and aegirine (dark pyroxenes), ilvaite (a black Ca–Fe silicate), its series partner manganbabingtonite, and the epidote and garnet (as andradite) on its Association line. A hardness match is any overlap of the printed ranges; a weight match is an in-water reading for a 20.00 g piece that overlaps babingtonite’s 14.01 to 14.07 g or lies within 0.05 g of it.
Result. Of 7 sheets, 2 match on both readings: augite, at 5.5 to 6 and 13.73 to 14.38 g, contains babingtonite on both; epidote, at 6 to 7 and 14.08 to 14.27 g, touches at hardness 6 and sits 0.02 g away. Hedenbergite, aegirine and ilvaite match on hardness alone; manganbabingtonite, at 6.5 to 7 and 14.21 g, and andradite, at 14.74 to 14.87 g, on neither. The methods are on how to test mineral hardness properly and how to measure specific gravity at home.
Documented failure: the balance cannot do it. The cleavage can. Babingtonite prints three cleavage forms, perfect {001} and good {010} and {100}; the augite sheet prints one good form, {110}, whose two directions meet at about 87°, plus partings; epidote prints perfect {001} and imperfect {100}. Colour does not help: augite lists black, epidote greenish black. Augite’s own placement is on is augite a pyroxene and epidote’s on is epidote a pyroxene.
How much of babingtonite’s iron is ferric? The iron split
In the ideal formula, exactly half. Ca2Fe2+Fe3+Si5O14(OH), formula mass 573.26 on standard atomic weights, works out at SiO2 52.40%, Fe2O3 13.93%, FeO 12.53%, CaO 19.56% and H2O 1.57%; the sheet’s ideal column prints 52.41, 13.93, 12.53, 19.56 and 1.57. Iron in total is 19.48% of the mass.
Worked on the sheet’s analyses. Converting oxide percentages to moles: the Arendal, Norway, analysis (FeO 7.68, Fe2O3 13.17, MnO 1.89, MgO 0.92) has 61% of its iron as Fe3+, and its divalent site holds 68% iron, 17% manganese and 15% magnesium. The Holyoke, Massachusetts, analysis (FeO 10.12, Fe2O3 14.43, MnO 1.03, MgO 0.65) has 56% ferric iron and a divalent site of 82% iron, 8% manganese and 9% magnesium.
Why the split matters for the name. The IMA list writes manganbabingtonite Ca2Mn2+Fe3+Si5O14(OH), with manganese where babingtonite has ferrous iron, and the sheet says the two form a series. Both analyses keep iron well ahead of manganese on that site. The sheets do not say how a specimen between them is to be named, and this page does not either. Of the 10 IMA rows written with Si5O14(OH), 3 carry babingtonite in their names.
Where is babingtonite found? Massachusetts and the other localities
The sheet’s Distribution line, in full. Known from a number of localities, most minor; some providing good crystals are: the Brastad mine, Oyestad, near Arendal, Norway; Grönsjöberg, Sweden; Herbornseelbach, Hesse, Germany; Baveno, Piedmont, Italy; the Khandivali quarry near Bombay, Maharashtra, India; Mitani, Kochi Prefecture, Japan; Noril’sk, western Siberia, Russia. In Massachusetts, exceptional crystals from Lane’s quarry, Westfield, Hampden Co.; the Cheapside and Deerfield quarries, East Deerfield, Franklin Co.; and Winchester Highlands, Uxbridge. Also Paterson and Mine Hill, New Jersey; the Goose Creek quarry, Leesburg, Virginia; and Lenoir, North Carolina.
Shared ground. Westfield (as the Lane quarry), Paterson and the Goose Creek quarry also appear on the datolite sheet’s Distribution line. The babingtonite sheet places it in cavities and vugs in mafic volcanic rocks, with prehnite and zeolites among its associates; the datolite sheet calls datolite a secondary mineral in mafic igneous rocks. This page names no locality the sheet does not.
Uses. No fetched source gives babingtonite a use, and this page claims none. The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.