Hedenbergite
Hedenbergite is CaFe2+Si2O6, the iron pyroxene of the diopside series: black to dark green, hardness 5.5–6.5, density 3.56, 22.51% iron. The Fe-majority check.
Hedenbergite is CaFe2+Si2O6 on the September 2026 IMA list: the iron member of the diopside series, a monoclinic calcium pyroxene, black to dark green, hardness 5.5–6.5, density 3.56, 22.51% iron. On the Handbook’s Elba and Dal’negorsk analyses, iron (with manganese, as the 1988 pyroxene report counts it) outweighs magnesium about 7 and 19 times: hedenbergite, not diopside.
In short
- The species. The Handbook of Mineralogy sheet gives monoclinic short prismatic crystals to 5 cm, columnar or acicular aggregates, granular and massive material; cleavage good on {110} at about 87°; hardness 5.5–6.5; density 3.56; black, dark green or green-brown; vitreous or dull; Pyroxene group. The September 2026 IMA-CNMNC Master List row reads CaFe2+Si2O6, status A, 1988 s.p., Sweden.
- The Fe-majority check. Morimoto et al. 1988, Nomenclature of pyroxenes (American Mineralogist 73, 1123) splits the calcium-rich band of the pyroxene quadrilateral, 45 to 50% Wo, into diopside and hedenbergite at its midpoint, counting Fe2+, Fe3+ and Mn together as ΣFe. Recast by script, the sheet’s Elba analysis is Wo 46.6, En 6.8, Fs 46.6 and its Dal’negorsk analysis Wo 50.0, En 2.5, Fs 47.5: magnesium is 0.127 and 0.051 of Mg + ΣFe. The diopside sheet’s two analyses give 0.979 and 0.931.
- Documented failure: the balance cannot place a mid-series piece. Hedenbergite reads 14.38 g in water for 20.00 g at its 3.56, diopside 13.79–14.08 g at 3.22–3.38, and johannsenite 13.88–14.35 g at 3.27–3.54. Johannsenite overlaps both, and an intermediate piece reads in between. The cell does check: Z = 4 in the printed cell gives 3.655 against the printed [3.65].
- Hedenbergite in quartz. Gems & Gemology, Fall 2024 Micro-World, “Hedenbergite in Quartz” (Liyan He and Wingtak Lui) describes groups of dark crystal inclusions shaped like a sea urchin in polished quartz, transparent to translucent, dark green to brownish green, identified as hedenbergite by Raman spectroscopy. The authors say material known in the trade as “urchin quartz” might contain inclusions other than hollandite. They name no locality, and neither does this page.
- Where it is found. The sheet calls it a common constituent of metamorphosed iron formations and common in Fe–Mn skarns. Its Distribution names Nordmark and Yxsjö, Sweden; Rio Marina, Elba; Seriphos, Greece; large crystals from Broken Hill, New South Wales; fine crystals from the Laxey mine, Idaho, and the Skardu area, Pakistan; and Dal’negorsk, Russia, among others. Five places on its list are on the ilvaite sheet too.
| Formula or analysis | Source | Wo | En | Fs (ΣFe) | Mg/(Mg + ΣFe) | Name by Fig. 4 | Density (measured) | 20.00 g in water | USGS best range, amp |
|---|---|---|---|---|---|---|---|---|---|
| CaFe2+Si2O6 | IMA hedenbergite row | 50 | 0 | 50 | 0 | Hedenbergite | 3.56 | 14.38 g | 0.20–0.40 (6 samples) |
| Tignitoio iron deposit, Elba | Hedenbergite sheet (1) | 46.6 | 6.8 | 46.6 | 0.127 | Hedenbergite | — | — | — |
| Dal’negorsk, Russia | Hedenbergite sheet (2) | 50.0 | 2.5 | 47.5 | 0.051 | Hedenbergite | — | — | — |
| Juva, Finland | Diopside sheet (1) | 49.2 | 49.7 | 1.0 | 0.979 | Diopside | — | — | — |
| Dutoitspan mine, Kimberley | Diopside sheet (2) | 45.4 | 50.8 | 3.7 | 0.931 | Diopside | — | — | — |
| CaMgSi2O6 | IMA diopside row | 50 | 50 | 0 | 1 | Diopside | 3.22–3.38 | 13.79–14.08 g | 0.40–0.60 (4 samples) |
| CaMnSi2O6 | IMA johannsenite row | — | — | — | — | Johannsenite (a separate IMA species) | 3.27–3.54 | 13.88–14.35 g | 0.30–0.40 (7 samples) |
What is hedenbergite? The calcium–iron pyroxene
Hedenbergite is CaFe2+Si2O6, the calcium pyroxene in which ferrous iron fills the place magnesium takes in diopside. The Handbook of Mineralogy hedenbergite sheet gives it monoclinic, point group 2/m, space group C2/c, as short prismatic crystals to 5 cm, in columnar or acicular aggregates, and granular, lamellar or massive. Twins are simple and polysynthetic on {100} and {010}. Cleavage is good on {110}, the two planes meeting at about 87°, with partings on {100} and {010}; fracture uneven to conchoidal; brittle; hardness 5.5–6.5; density 3.56 measured.
Colour and optics. Black, dark green or green-brown, brownish green in thin section; vitreous or dull. The sheet prints no streak, so this page gives none (how to use a streak plate). Biaxial (+), α = 1.732, β = 1.739, γ = 1.757, 2V = 63°, with weak pleochroism from pale green to yellow-green. The Name field honours the Swedish chemist M.A. Ludwig Hedenberg, who first described the species.
What the lists record. The September 2026 IMA-CNMNC Master List gives CaFe2+Si2O6, status A, 1988 s.p., Sweden; 1988 is also the year of the IMA pyroxene report. The sheet’s ideal column, 48.44 SiO2, 22.60 CaO and 28.96 FeO, reproduces from the formula on standard atomic weights; worked, the formula is 22.51% iron, the figure the ilvaite page uses. the 1988 IMA pyroxene report reads ferrosalite, funkite, hudsonite and lotalite as hedenbergite, and ferrohedenbergite and aegerine-hedenbergite as augite (Table 6, read from the rendered page). The general pyroxene question is on is spodumene a pyroxene and is augite a pyroxene.
Hedenbergite or diopside? The Fe-majority check
A calcium pyroxene with more iron than magnesium is hedenbergite; with more magnesium, diopside. Both sheets say the two form a series. The 1988 report plots calcium–magnesium–iron pyroxenes on the Wo–En–Fs quadrilateral, normalised to Ca + Mg + ΣFe = 100 with ΣFe = Fe2+ + Fe3+ + Mn, and its Fig. 4 divides the band from 45 to 50% Wo into diopside and hedenbergite at the midpoint between En and Fs. Below 45% Wo the name is augite, whose three borders are on its own page and are not repeated here.
The check, worked on the sheets. Recast to six oxygens, the hedenbergite sheet’s Tignitoio iron deposit, Elba analysis gives Ca 0.90, Mg 0.13, Fe2+ 0.77, Fe3+ 0.10 and Mn 0.03, the same numbers as the sheet’s own formula line: Wo 46.6, En 6.8, Fs 46.6, and Mg/(Mg + ΣFe) 0.127. The Dal’negorsk analysis gives Ca 0.99, Mg 0.05, Fe2+ 0.78, Fe3+ 0.03 and Mn 0.13: Wo 50.0, En 2.5, Fs 47.5, and 0.051. Leaving manganese out of ΣFe changes these to 0.130 and 0.059; iron still dominates. The diopside sheet’s Juva and Dutoitspan analyses give 0.979 and 0.931, on the magnesium side. All four sit inside 45 to 50% Wo.
Documented failure: what the hand cannot see. Colour does not settle it: the diopside sheet includes dark green and black, the hedenbergite sheet black and dark green. Weight narrows it but does not close it: 20.00 g reads 14.38 g in water as hedenbergite, 13.79–14.08 g as diopside, and 13.88–14.35 g as johannsenite, CaMnSi2O6, the third member named on both sheets’ series lines. The printed cell, 450.8 ų with Z = 4, gives 3.655 against the printed [3.65], and the diopside cell 3.280 against 3.278, so the end members are well defined; an intermediate piece is not. The method is on how to measure specific gravity at home. The diopside page’s chromium line is not repeated here.
Hedenbergite in quartz: what Gems & Gemology found
Hedenbergite occurs as dark green inclusions in quartz, identified by Raman spectroscopy in a 2024 Gems & Gemology note. Gems & Gemology, Fall 2024 Micro-World, “Hedenbergite in Quartz” (Liyan He and Wingtak Lui) reports that, in a large group of polished quartz samples, the authors observed groups of dark crystal inclusions that took the shape of a sea urchin. Where a crystal reached the surface its cross section was rhomboid, indicating monoclinic symmetry; under magnification the inclusions were transparent to translucent and dark green to brownish green. Raman spectra identified them as hedenbergite, confirmed against the RRUFF database. In the same samples they identified a yellow to light brown inclusion as sphalerite.
What the note does and does not say. It says that, based on earlier work, the material known in the trade as “urchin quartz” might contain inclusions other than hollandite. It gives no locality for the quartz, so this page names none; the hedenbergite sheet lists quartz among its associates in granites and syenites, and names Seriphos, Greece, among its localities, but neither source ties the two. The note does not discuss benefits, meanings or any property beyond identification, and nor does this page. The quartz itself is on quartz; inclusions in general are touched on in what is a phantom crystal.
Magnetism, for scale. The sheet prints no magnetic property. USGS Open-File Report 99-529, Table 1 pulled 6 hedenbergite samples on a laboratory separator at 0.10–0.50 amp, best 0.20–0.40, against diopside’s best 0.40–0.60 and johannsenite’s 0.30–0.40; the report’s definitions call that paramagnetic, not ferromagnetic. The magnet question at large is on which minerals are magnetic.
Where is hedenbergite found? Skarns, iron formations and the ilvaite places
The Occurrence field: a common constituent of metamorphosed iron formations or other ferruginous siliceous sediments; common in Fe–Mn skarns; in alkalic granites, syenites, and xenoliths in kimberlite. Its associates are grunerite (iron formations) and arfvedsonite, quartz and fayalite (granites, syenites).
The Distribution, as printed. A few localities for studied material include Nordmark, Värmland, and Yxsjö, Örebro, Sweden; Prägraten, Tirol, Austria; Fürstenberg, Saxony, Germany; Rio Marina, Elba, Italy; Seriphos, Greece; in the USA, Iron Hill, Gunnison Co., Colorado, fine crystals from the Laxey mine, South Mountain, Owyhee Co., Idaho, the Pima district and the Westinghouse mine, Arizona, and Hanover, New Mexico; the Vesturhorn intrusion, southeast Iceland; large crystals from Broken Hill, New South Wales; the Obira mine, Bungo, Oita Prefecture, Japan; Tirodi and Kacharwali, India; fine crystals from the Skardu area, Pakistan; and Dal’negorsk, Primorskiy Kray, Russia. We add no other locality.
The ilvaite places. By script over the two Distribution fields, five places appear on both the hedenbergite and ilvaite sheets: Rio Marina on Elba, Seriphos, the Laxey mine in Idaho, the Obira mine in Japan, and Dalnegorsk. The ilvaite sheet lists hedenbergite among its associates, in contact metasomatic rocks and iron deposits; the hedenbergite sheet’s association line does not name ilvaite. The dark silicates side by side are on babingtonite. Hazard questions about any mineral are routed to toxic minerals in a collection; nothing here is health or safety advice. More species are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.