Almandine
Almandine is the iron-aluminium garnet, Fe2+3Al2(SiO4)3: cubic, hardness 7 to 7.5, density 4.318, one index of 1.830. Its Falun analysis is 15% pyrope, worked.
Almandine is the iron-aluminium garnet, Fe2+3Al2(SiO4)3 on both the IMA list and the Handbook sheet: cubic, hardness 7 to 7.5, density 4.318, one refractive index of 1.830, no cleavage. The sheet calls it the most common garnet, in mica schists and gneisses. Its Falun, Sweden analysis works out at 81.5% iron and 15.4% magnesium at the garnet's X site.
In short
- Garnet is a group; almandine is a species. The September 2026 IMA-CNMNC Master List lists almandine as Fe2+3Al2(SiO4)3, status G, with the year printed as 1546 ? and the country as Turkey. The list has no group column. Grew and co-authors, American Mineralogist 98 (2013), the IMA garnet report, placed 14 species in the garnet group; a script finds a row for all 14 on the 2026 list. The word garnet has no row of its own.
- The magnesium check. The Handbook of Mineralogy sheet’s Falun analysis has 3.85% MgO, but its printed formula line lists iron, manganese and calcium only, summing to 2.68 at a site that holds 3. Worked from the printed oxides on 12 oxygens, magnesium is 0.46 and the site fills to 2.99: 81.5% iron, 15.4% magnesium. The Falun garnet is still almandine, about one-sixth of the way to pyrope.
- One index, and a high one. Almandine is cubic and prints a single refractive index, n = 1.830, above spessartine’s 1.800, grossular’s 1.734 and pyrope’s 1.714 on their sheets. Ruby is a different species, settled by the rule on the corundum page; the home sequence is on how to tell if garnet is real.
- Heaviest of the six garnet sheets used here. Measured density 4.318 against spessartine 4.190, andradite 3.8 to 3.9, uvarovite 3.77 to 3.81, grossular 3.594 and pyrope 3.582. A 20.00 g piece reads 15.37 g in water.
- Crystals to 1 m, on the sheet: well-formed dodecahedra or trapezohedra in mica schists and gneisses. Its Distribution field names the Zillertal, Austria; Falun, Sweden; Broken Hill, New South Wales; and a large commercial deposit at the Barton mine, North Creek, New York. It names no British locality.
| Site and cation | Oxide in the analysis (wt%) | Per formula, worked | Per formula, as printed on the sheet | Share of the X site, worked | End-member it points to |
|---|---|---|---|---|---|
| X: iron (Fe2+) | FeO 36.37 | 2.43 | 2.49 | 81.5% | Almandine, Fe2+3Al2(SiO4)3 |
| X: magnesium | MgO 3.85 | 0.46 | Not printed | 15.4% | Pyrope, Mg3Al2(SiO4)3 |
| X: manganese | MnO 0.86 | 0.06 | 0.14 | 2.0% | Spessartine, Mn2+3Al2(SiO4)3 |
| X: calcium | CaO 0.41 | 0.04 | 0.05 | 1.2% | Grossular, Ca3Al2(SiO4)3 |
| X site total (ideal 3) | 2.99 | 2.68 | 100% (rounded) | Iron-dominant: almandine | |
| Y site: Al, Fe3+, Ti (ideal 2) | Al2O3 20.72, Fe2O3 0.83, TiO2 0.16 | 1.95 + 0.05 + 0.01 = 2.01 | 1.94 + 0.05 + 0.01 = 2.00 | Agrees with the sheet | |
| Z site: Si, Al (ideal 3) | SiO2 37.39 | 2.99 + 0.01 = 3.00 | 2.99 + 0.01 = 3.00 | Agrees with the sheet |
What is almandine? The iron garnet, and what garnet means
The names. The September 2026 IMA-CNMNC Master List writes almandine Fe2+3Al2(SiO4)3, status G, grandfathered, with the year printed as 1546 followed by a question mark, the country as Turkey, and the first reference given as original paper?. The Handbook sheet prints the same formula and the mineral group line Garnet group. Its Name field: for Alabanda in Turkey, a cutting center in antiquity. The IMA garnet report adds that the name was first used by D.L.G. Karsten in 1800.
Garnet, the group. Grew and co-authors, American Mineralogist 98 (2013), approved by the IMA commission, defined a garnet supergroup of 32 approved species with the general formula {X3}[Y2](Z3)φ12, and divided it into groups by the total charge at the Z site. Its garnet group, with charge 12, lists 14 species: almandine, andradite, calderite, eringaite, goldmanite, grossular, knorringite, majorite, menzerite-(Y), momoiite, morimotoite, pyrope, spessartine and uvarovite. A script over the 2026 IMA list finds a row for every one of them; species approved after 2013 are not counted here, because the list prints no group. Almandine’s end-member is {Fe2+3}[Al2](Si3)O12.
What it looks like, per the sheet. Cubic, typically well-formed dodecahedra or trapezohedra to 1 m, also rounded grains and massive. Deep red, brownish red, red-violet or black, sometimes sectored, with a white streak and a vitreous to resinous lustre. There is no cleavage, only a parting on {110}, read from the rendered sheet. GIA names almandine among the five garnets it calls commercially important as gems, with pyrope, spessartine, grossular and andradite.
Is my garnet almandine or pyrope? The magnesium check, worked
The rule, as arithmetic. A garnet’s name follows the cation that dominates its X site; the IMA report shows the aluminium garnets dividing by whether iron, manganese, magnesium or calcium dominates there. Pure almandine is 33.66% iron by mass on standard atomic weights (43.30% FeO), the figure the sheet prints as its second, ideal analysis.
Worked on the sheet. The Falun analysis reads SiO2 37.39, TiO2 0.16, Al2O3 20.72, Fe2O3 0.83, FeO 36.37, MnO 0.86, MgO 3.85, CaO 0.41, total 100.59. Dividing each oxide by its formula mass and scaling to 12 oxygens gives silicon 2.99, a Y site of 2.01 and an X site of iron 2.43, magnesium 0.46, manganese 0.06 and calcium 0.04, total 2.99. The sheet’s printed line agrees on the Y and Z sites to 0.01, but gives the X site as iron 2.49, manganese 0.14 and calcium 0.05, sum 2.68, with no magnesium. We do not know why; the oxides, as printed, carry 0.46 magnesium.
What the check shows. Iron is 81.5% of the X site and magnesium 15.4%, so the Falun garnet is almandine carrying about a sixth pyrope component, consistent with the sheet’s note that almandine forms a series with pyrope. The International Gem Society says 80% is about the highest purity typically met in almandine. The manganese side of the same rule, and how far a refractometer can take it, is on spessartine.
How to tell almandine from the other red garnets, ruby and spinel
Against the other garnets. On their Handbook sheets, almandine prints n = 1.830 and density 4.318; spessartine 1.800 and 4.190; grossular 1.734 and 3.594; pyrope 1.714 and 3.582. Worked as 20 − 20/D, a 20.00 g piece reads 15.37 g in water as almandine, 15.23 g as spessartine and 14.42 g as pyrope. A mixed garnet, like Falun’s, sits between its end-members, so a reading names a direction, not a species.
Against ruby. Ruby is corundum, hardness 9, and gives two refractometer readings; the rule for a red stone is set out on corundum and is not repeated here. Against spinel: the Handbook spinel sheet prints one index, n = 1.719, and octahedral crystals, where the garnet sheets print dodecahedra and trapezohedra. The full home sequence is on how to tell if garnet is real.
Rhodolite. GIA calls rhodolite a purple-red garnet, and the International Gem Society describes it as a blend of pyrope and almandine. It has no row on the IMA list, by script; it is a trade name for a composition between two species. The pink-silicate question is on is rhodonite a garnet.
Where almandine is found: the Zillertal, Falun, Broken Hill and North Creek
The Occurrence field calls almandine the most common garnet, typically in mica schists and gneisses, from regionally metamorphosed argillaceous sediments and pelites; also in contact-metamorphic hornfels, granites and eclogites, sedimentary rocks, and as a detrital mineral. Its associates include biotite, cordierite, chlorite, staurolite, andalusite, kyanite, sillimanite and hematite.
The Distribution field opens widespread; some localities for fine crystals include and names: the Zillertal, Tirol, Austria; Falun, Sweden; near Bodø, Norway; the Akhmatovsk deposit near Zlatoust, Ural Mountains, Russia; Roxbury and Southbury, Connecticut; Auburn and Topsham, Maine; Westfield and Russell, Massachusetts; Hanover, New Hampshire; Avondale, Pennsylvania; a large commercial deposit at the Barton mine, North Creek, New York; Michigamme, Michigan; Salida, Colorado; Fort Wrangell, Alaska; Pernambuco, Bahia, Brazil, as the sheet prints it; the Miami district, Zimbabwe; Broken Hill and Thackaringa, New South Wales, and the Harts Range, Northern Territory; and Yamanoo and the Ishikawa district, Japan.
In Britain the sheet names nothing, and we add nothing. The International Gem Society mentions almandine from Gore Mountain, New York, reaching 60 cm across. 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.