Is vesuvianite a garnet?
No: vesuvianite is a tetragonal or monoclinic mineral, not one of the 32 garnet species, though one old garnet label means it. Which test fits your specimen.
No. Vesuvianite, (Ca,Na)19(Al,Mg,Fe)13(SiO4)10(Si2O7)4(OH,F,O)10 on the IMA list, is tetragonal or monoclinic and is not one of the 32 garnet-supergroup species. It grows with grossular at nearly the same hardness, 6 to 7, and one refractometer reading cannot separate them: grossular’s 1.734 sits inside vesuvianite’s 1.700 to 1.752.
In short
- The verdict. Grew et al., American Mineralogist 98 (2013) define the garnet supergroup as all minerals isostructural with garnet and list 32 species; vesuvianite is not one. By script, 0 of their 32 have Si2O7 in their IMA formula, while 8 IMA rows, vesuvianite among them, contain (SiO4)10(Si2O7)4. The Handbook of Mineralogy sheet gives vesuvianite as tetragonal or monoclinic; the garnet-group sheets are cubic.
- The pyramidal garnet trap. Grew et al.’s Appendix 2, 715 old and varietal garnet names, decodes pyramidal garnet as vesuvianite (Manutchehr-Danai 2009): the one entry that does, by script. A specimen labelled pyramidal garnet is vesuvianite and not a garnet.
- Choose the test by the specimen. Sharp crystals: square prisms against dodecahedra. Loose clean stones: the balance, 13.98 to 14.17 g in water for 20.00 g against grossular’s 14.44 g. Cut stones: the polariscope and the 0.015 line. Hardness, 6 to 7 against 6.5 to 7, chooses nothing.
- The 0.015 line, and where it fails. Grew et al. report birefringent grossular–andradite garnets at 0.001 to 0.010, up to 0.015. The International Gem Society gives vesuvianite 0.001 to 0.025. A birefringence above 0.015 rules out the garnet group; below it, nothing is decided. Holtstamite, a tetragonal garnet, is uniaxial with 0.030.
- Names that cross the line. Californite is grossular-katoite to Grew et al., a mixture of idocrase and grossular to the gem society, and filed under idocrase by Hobbs, Gems and Gemology, Spring 1982. Wiluite is an IMA vesuvianite-type species, 1997-026, but wiluite of Severgin is grossular in the garnet report. Read the label with its source.
| Test | Vesuvianite | Grossular | Andradite | Does it choose? | Wrong for (documented failure) |
|---|---|---|---|---|---|
| Crystal system and shape | Tetragonal or monoclinic; short pyramidal to long prismatic (sheet) | Cubic; dodecahedra or trapezohedra (sheet) | Cubic; dodecahedra, trapezohedra (sheet) | Yes, on sharp crystals | Massive and granular material; holtstamite and henritermierite are tetragonal garnets (Grew) |
| One refractometer reading | ω 1.703 to 1.752, ε 1.700 to 1.746 (sheet); 1.655 to 1.795 (IGS) | 1.734 (sheet) | 1.887 (sheet) | Andradite only, by 0.135 | Grossular: 1.734 lies inside vesuvianite’s range |
| Birefringence: the 0.015 line | 0.001 to 0.025 (IGS) | 0.001 to 0.010, rarely 0.015 (Grew) | Typically weakly anisotropic (sheet) | Yes, if above 0.015 | Low-birefringence vesuvianite; holtstamite 0.030 (Grew) |
| Optic character | Uniaxial (−); uniaxial (+) and biaxial common (sheet) | Isotropic, weak strain birefringence (sheet); birefringent ones normally biaxial (Grew) | Isotropic (sheet) | Not alone | Biaxial vesuvianite; uniaxial holtstamite |
| 20.00 g piece in water | 3.32 to 3.43: 13.98 to 14.17 g (sheet); to 3.47, 14.24 g (IGS) | 3.594: 14.44 g | 3.8 to 3.9: 14.74 to 14.87 g | Yes, on clean single-species pieces | Californite (IGS 3.25 to 3.32; Hobbs 3.40 ± 0.10) and matrix specimens |
| Hardness | 6 to 7 | 6.5 to 7 | 6.5 to 7 | No | Every specimen |
| IMA formula | (SiO4)10(Si2O7)4 (IMA) | Ca3Al2(SiO4)3 | Ca3Fe3+2(SiO4)3 | Yes, with an analysis | Needs an analysis |
| The label name | Idocrase; pyramidal garnet (Grew) | Viluite; wiluite of Severgin (Grew) | Demantoid, melanite, topazolite | Only with the source | Californite and wiluite each have more than one meaning |
Is vesuvianite a garnet? Choose by structure, not by look
Vesuvianite is not a garnet: it is not isostructural with garnet, and the IMA garnet report’s 32 species do not include it. Grew et al., American Mineralogist 98 (2013) define the garnet supergroup as all minerals isostructural with garnet, with the general formula {X3}[Y2](Z3)φ12. The September 2026 IMA-CNMNC Master List lists vesuvianite as (Ca,Na)19(Al,Mg,Fe)13(SiO4)10(Si2O7)4(OH,F,O)10, A, 1962 s.p., Italy. A script finds the IMA rows of all 32 supergroup species and 0 with Si2O7 in the formula; it finds 8 rows containing (SiO4)10(Si2O7)4: alumovesuvianite, cyprine, fluorvesuvianite, magnesiovesuvianite, manganvesuvianite, modraite, vesuvianite and wiluite.
What the two sheets say. The Handbook vesuvianite sheet writes Ca19(Al,Mg)13B0–5Si18O68(OH,O,F)10, tetragonal or monoclinic, point group 4/m 2/m 2/m or 2/m, short pyramidal to long prismatic crystals to 15 cm, with up to 30 forms reported on one crystal. The grossular and andradite sheets are cubic, point group 4/m -3 2/m. Reading silicate units in a formula is set out on is epidote a pyroxene; its test is not repeated here.
Why the question gets asked. The vesuvianite sheet lists grossular first among its associates, and the andradite sheet lists vesuvianite first among its own. The International Gem Society idocrase article says that, properly cut, it is as bright as the grossular garnets it so strongly resembles, and often intergrown with grossular. The species page is vesuvianite.
Pyramidal garnet, californite, wiluite: names that cross the line
The pyramidal garnet trap: the IMA garnet report’s own list of garnet names includes one that means vesuvianite. Grew et al.’s Appendix 2 gives 715 synonyms, obsolete, varietal and discredited names for the garnet supergroup, and decodes pyramidal garnet as vesuvianite, citing Manutchehr-Danai (2009). A script finds it the only entry of the 715 that mentions vesuvianite, and none for idocrase. A label reading pyramidal garnet names a vesuvianite.
Californite has three readings. Appendix 2 decodes californite as grossular-katoite. The International Gem Society grossular article calls it a mixture of idocrase (vesuvianite) and grossular garnet, from California, Pakistan and South Africa, and its idocrase article gives density 3.25 to 3.32. Hobbs, Gems and Gemology, Spring 1982 files californite under idocrase in his table of jade simulants, with the misleading names American jade and California jade, index 1.713 to 1.718 and SG 3.40 ± 0.10. We print all three. Jade itself is on is jade a mineral.
Wiluite has two. The IMA list has wiluite as a species, Ca19(Al,Mg)13(B,☐,Al)5(SiO4)10(Si2O7)4(O,OH)10, A, 1997-026, Russia, one of the 8 vesuvianite-type rows. Appendix 2 decodes wiluite of Severgin, and viluite, as grossular. The gem society uses both senses: green idocrase crystals from the Wilui River known as wiluite, and opaque green grossular crystals from the Wilui River also known as viluite. Idocrase itself has no IMA row, by script; the gem society heads its article Idocrase (Vesuvianite).
Can a refractometer tell vesuvianite from garnet? The 0.015 line
One reading cannot: grossular’s single index, 1.734, lies inside vesuvianite’s ranges, ω 1.703 to 1.752 and ε 1.700 to 1.746. Andradite, at 1.887, sits 0.135 above vesuvianite’s highest on the sheets. The gem society widens vesuvianite to 1.655 to 1.795, depending on paragenesis, which still leaves andradite 0.092 above.
The 0.015 line: a birefringence above 0.015 is above anything Grew et al. report for a birefringent grossular–andradite garnet. They say such garnets are normally biaxial, with low to moderate birefringence of 0.001 to 0.010, and that up to 0.015 has been observed with considerable andradite component. The gem society gives vesuvianite 0.001 to 0.025. Above 0.015, the stone is not a garnet-group grandite. At or below it, birefringence chooses nothing, and the documented failure runs the other way too: GIA gives garnet birefringence none.
The holtstamite exception. Grew et al. place two tetragonal, OH-bearing species, henritermierite and holtstamite, in the garnet supergroup, and say holtstamite is uniaxial with a high birefringence, 0.030. The holtstamite sheet prints ω 1.718 and ε 1.746, both inside vesuvianite’s ranges, and gives only the Wessels mine, Kalahari manganese field, South Africa. Its sheet describes rounded composite grains to 3 mm. A uniaxial reading with strong birefringence therefore points away from the garnet group, not away from the garnet supergroup.
Weight and hardness: what they can and cannot choose
On clean single-species pieces the balance chooses, and hardness never does. Worked as 20 − 20/D, a 20.00 g vesuvianite reads 13.98 to 14.17 g in water on its sheet; grossular 14.44 g; andradite 14.74 to 14.87 g. The vesuvianite species page makes the grossular gap its own case and is linked rather than repeated: vesuvianite. The method is on how to measure specific gravity at home.
Where the scale fails. The gem society’s vesuvianite density reaches 3.47, 14.24 g, narrowing the gap to grossular to 0.20 g, and it says mixtures with other gem species have other SG figures. Californite, the idocrase–grossular mixture, reads 3.25 to 3.32 on its figures and 3.40 ± 0.10 on Hobbs’s; a mixture weighs as a mixture. A crystal on calcite matrix cannot be weighed as either.
Hardness. Vesuvianite is 6 to 7, grossular and andradite 6.5 to 7 on their sheets: a scratch test separates none of them. See how to test mineral hardness properly.
Who each test is wrong for
Each test short of an analysis fails on some specimen, so choose the test that fits the piece in hand. Shape is right for a sharp crystal and wrong for massive or granular material, and for the two tetragonal garnets. A single refractometer reading is right against andradite and wrong against grossular. The 0.015 line is right for a strongly birefringent stone and silent below it. The balance is right for a clean, loose crystal and wrong for californite, matrix pieces and mixtures. An analysis is decisive and rarely available.
The label is wrong more often than the stone. Pyramidal garnet means vesuvianite; idocrase means vesuvianite; californite and wiluite each carry more than one meaning, depending on which source the labeller followed. When an old label says garnet on a square-sectioned prism, the label is the thing to correct; how to keep the old name beside the new is on what ex coll means on a mineral label.
On this site, the garnet side is on is andradite a garnet, grossular and how to tell if garnet is real; the classification questions are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.