Andradite
Andradite, Ca3Fe3+2(SiO4)3, is the calcium iron garnet: hardness 6.5 to 7, density 3.8 to 3.9, index 1.887. Demantoid, topazolite, and where melanite ends.
Andradite is the calcium iron garnet, Ca3Fe3+2(SiO4)3: cubic, hardness 6.5 to 7, density 3.8 to 3.9, one refractive index of 1.887. Demantoid, topazolite and melanite are its variety names, per the International Gem Society and the IMA garnet report. Worked on the schorlomite join, black titanian andradite stays andradite below about 15 wt% TiO2.
In short
- One species of the garnet group. The September 2026 IMA-CNMNC Master List lists andradite as Ca3Fe3+2(SiO4)3, grandfathered, 1868, Norway. Grew et al., American Mineralogist 98 (2013), the IMA garnet report, places it among the 14 species of the garnet group, total charge 12 at the tetrahedral site, with end-member {Ca3}[Fe3+2](Si3)O12. The Handbook of Mineralogy sheet names two series: with grossular and with schorlomite.
- The 15 percent line. Grew et al. say titanian andradite is often called melanite and quote the most-used test for schorlomite as Ti greater than Fe3+ at the Y site, approximately the same as TiO2 above 15 wt% (Zedlitz 1933). Worked on the simple andradite–schorlomite join, Ti equals Fe3+ at Y at 15.13 wt% TiO2; the schorlomite end-member is 29.16%.
- Melanite is andradite on that test. The International Gem Society says melanites contain 1 to 5% titanium oxide and are black. On the join, 5 wt% TiO2 puts 0.32 Ti at Y against 1.68 Fe3+: far below the line. Grew et al.’s own primary criterion is that the schorlomite component be the most abundant; the 15% figure is the approximation they quote.
- Names decoded, IMA rows checked. Grew et al.’s list of 715 garnet names decodes demantoid, topazolite, melanite, colophonite and Siberian chrysolite as andradite. A whole-line scan of the IMA list finds 0 lines containing demantoid, topazolite or colophonite, and none with a melanite row.
- Documented failure: horsetails. The International Gem Society says horsetail inclusions were long considered diagnostic for demantoid, but a 2018 study found them in non-demantoid brown andradite. By weight, 14.74 to 14.87 g in water for 20.00 g, andradite overlaps the schorlomite sheet’s 14.58 to 14.85 g; the index, 1.887 against 1.94 to 1.98, separates them.
| Name or material | What it is (source) | TiO2, wt% | Refractive index | Density; 20.00 g piece in water | IMA row? |
|---|---|---|---|---|---|
| Andradite, Ca3Fe3+2(SiO4)3 | End-member; garnet group (sheet; Grew) | 0 | 1.887 (sheet) | 3.8 to 3.9; 14.74 to 14.87 g | Yes: G, 1868, Norway |
| Reškovic stream, Serbia | Sheet analysis (1): Fe3+ 1.94, Al 0.02 at Y | Trace | - | - | As andradite |
| Demantoid | Green andradite, named for its diamond-like appearance (IGS); andradite (Grew, Appendix 2) | Not stated | 1.881 to 1.888 (IGS) | 3.82 to 3.88 (IGS); 14.76 to 14.85 g | No |
| Topazolite | Yellow to yellowish green andradite (IGS); andradite (Grew, Appendix 2) | Not stated | 1.887 (IGS); San Benito 1.855 to 1.877 (IGS) | San Benito 3.77 to 3.81 (IGS); 14.69 to 14.75 g | No |
| Melanite | Black andradite with 1 to 5% titanium oxide (IGS); andradite (Grew, Appendix 2) | 1 to 5 (IGS) | 1.89 (IGS) | About 3.9 (IGS); 14.87 g | No |
| Colophonite | Granular, usually brown andradite with a resinous lustre (IGS); andradite (Grew) | Not stated | - | - | No |
| The line: Ca3(TiFe3+)(Si2Fe3+)O12 | Ti = Fe3+ at Y on the join, worked; Grew quotes TiO2 above 15 wt% as approximately the same test | 15.13, worked | - | - | - |
| Schorlomite, Ca3Ti2(SiFe3+2)O12 | Schorlomite group, Z charge 10 (Grew); garnet group on its sheet | 29.16, worked (end-member) | 1.94 to 1.98, increasing with Ti (sheet) | 3.69 to 3.88; 14.58 to 14.85 g | Yes: G, 1846, USA |
| Grossular, Ca3Al2(SiO4)3 | The other series end on the sheet | 0 | 1.734 (sheet) | 3.594; 14.44 g | Yes: A, 1962 s.p., Russia |
What is andradite? The calcium iron garnet
Andradite is the garnet with calcium at the X site and ferric iron at the Y site, Ca3Fe3+2(SiO4)3. The September 2026 IMA-CNMNC Master List gives it status G, grandfathered, 1868, Norway. On standard atomic weights the formula mass is 508.17 and the composition 33.11% CaO, 31.42% Fe2O3 and 35.47% SiO2, which is the sheet’s ideal column to the second decimal; iron is 21.98% of the mass. GIA’s garnet description names andradite among the five garnet species that are commercially important as gems.
Where it sits in the IMA scheme. Grew et al., American Mineralogist 98 (2013) define the garnet supergroup as all minerals isostructural with garnet, 32 approved species with the general formula {X3}[Y2](Z3)φ12, split into groups by the total charge at the Z site. Andradite is in the garnet group, charge 12, written {Ca3}[Fe3+2](Si3)O12. They record the oldest descriptions as allochroite of de Andrada and melanite of Werner, both in 1800. Whether andradite is a garnet, tested site by site, is on is andradite a garnet.
What the sheet records. Cubic, point group 4/m -3 2/m; commonly well-crystallized dodecahedra, trapezohedra or combinations, to 5 cm, and granular to massive. Fracture uneven to conchoidal, brittle, no cleavage printed. Hardness 6.5 to 7; density 3.8 to 3.9 measured, 3.859 calculated. Isotropic, typically weakly anisotropic, n = 1.887. Yellow, greenish yellow to emerald-green, dark green, brown, brownish red, brownish yellow, grayish black or black, and may be sectored; streak white; lustre adamantine to resinous, dull. A ligature-aware search of the sheet finds no fluorescence.
Is melanite andradite? The 15 percent line
The 15 percent line: on the simple andradite–schorlomite join, titanium overtakes ferric iron at the Y site at 15.13 wt% TiO2, and below that a black titanian garnet is andradite. Grew et al., American Mineralogist 98 (2013) say chemical data on Ti-bearing andradite, often called by the varietal name melanite, show TiO2 ranging continuously from 0 to 19 wt%. Among the criteria most often used to separate schorlomite from Ti-bearing andradite they quote Ti greater than Fe3+ at Y (Ito and Frondel 1967; Deer et al. 1982), approximately the same as TiO2 above 15 wt% (Zedlitz 1933).
Worked. Write the join as Ca3(Ti2s Fe3+2−2s)(Si3−2s Fe3+2s)O12, with s the schorlomite fraction. At s = 0.5 the formula is Ca3(TiFe3+)(Si2Fe3+)O12, mass 527.95, with 15.13% TiO2: the two criteria agree. The IMA schorlomite end-member, Ca3Ti2(SiFe3+2)O12, is 29.16% TiO2. The International Gem Society says melanites contain 1 to 5% titanium oxide; on the join 1% is s = 0.03 and 5% is s = 0.16, at most 0.32 Ti at Y. The model ignores aluminium, magnesium and ferrous iron, which real analyses carry; Grew et al.’s own primary test is that the generalised schorlomite component be the most abundant, computed with their spreadsheet.
Where to look, and what fails. The andradite sheet says it occurs in alkalic igneous rocks, then typically titaniferous. The schorlomite sheet, Ca3(Ti4+,Fe3+)2(Si,Fe3+)3O12, gives n = 1.94 to 1.98, increasing with Ti content, and density 3.69 to 3.88: 14.58 to 14.85 g in water for 20.00 g, inside andradite’s range, so the balance cannot split them. The schorlomite sheet calls it garnet group; Grew et al. place it in a schorlomite group. Both share Magnet Cove, Arkansas and the Gem mine area, San Benito County, California on their Distribution fields.
Demantoid, topazolite, colophonite: the variety names decoded
Demantoid, topazolite, melanite and colophonite are all andradite. The International Gem Society andradite article calls demantoid the best-known variety, topazolite yellow to yellowish green, melanite black with 1 to 5% titanium oxide, and colophonite a granular, usually brown, reddish or orangish andradite with a resinous lustre. Grew et al.’s Appendix 2, a list of 715 synonyms and varietal names, decodes each as andradite. The IMA list has a row for none of them, by script.
Trade names. The International Gem Society demantoid article says demantoids have been offered under names such as Siberian emeralds, Siberian chrysolites and Ural chrysolites. Appendix 2 decodes Siberian chrysolite and smeraldo degli Urali as andradite. A label using one of these names on a green garnet should be read as andradite, and on a non-garnet as whatever the specimen actually is.
Two documented disagreements. The gem society says horsetail inclusions long counted as diagnostic for demantoid, but that a 2018 study found them in brown, non-demantoid andradite, and not all demantoids have them. It credits the name to Nils Gustaf Nordenskiöld in 1854; Appendix 2 attributes demantoid to Nils Adolf Erik Nordenskiöld, citing Chester (1896), and its authors warn that many attributions are secondary and do not refer to the first use. Both are printed here. This page gives no colour cause for any variety.
Andradite, grossular and uvarovite
Andradite shares its calcium X site with grossular and uvarovite and differs at Y. The andradite sheet names a series with grossular; grossular reads 1.734 and 14.44 g in water for 20.00 g, against andradite’s 1.887 and 14.74 to 14.87 g, so both index and weight separate the end-members. The grossular page sets out the six calcium garnets; its ladder is not repeated here. Mali garnet, a blend of the two, is discussed there.
Against uvarovite the balance fails. The uvarovite sheet gives 3.77 to 3.81 and n = 1.865: 14.69 to 14.75 g in water, overlapping andradite at 14.74 to 14.75 g. The index differs by 0.022. Green-garnet separation is the subject of is tsavorite a garnet; the red garnets are on how to tell if garnet is real.
Magnetism is not printed on the sheet; the USGS separator figures for andradite are on is andradite a garnet.
Where andradite is found
The Occurrence field: in skarns from contact metamorphosed impure limestones or calcic igneous rocks; in chlorite schists and serpentinites; in alkalic igneous rocks, then typically titaniferous. Associates are vesuvianite, chlorite, epidote, spinel, calcite, dolomite and magnetite. The vesuvianite question is on is vesuvianite a garnet.
The Distribution field calls andradite widespread and names fine examples from Frascati, Alban Hills, Lazio; the Val Malenco, Lombardy; the Ala Valley, Piedmont; and Larcinaz, Val d’Aosta, Italy; Dognecea and Oraviţa, Banat, and Ocna de fier, Romania; Zermatt, Switzerland; Arendal, Norway; the Wessels mine, near Kuruman, South Africa; gem crystals from the Bobrovka River, Nizhni Tagil district, and the Sissertsk district, Urals; Stanley Butte, Arizona; Garnet Hill and the Gem mine area, California; Franklin and Sterling Hill, New Jersey; Magnet Cove, Arkansas; Prince of Wales Island, Alaska; and near Charco de Peña, Chihuahua, Mexico.
Cross-checks. The International Gem Society’s demantoid localities agree with the sheet at Val Malenco, Ala and the Urals; its Namibian and Madagascan sources are not on the sheet, and we add 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.