Titanite
Titanite is calcium titanium silicate, CaTiO(SiO4): monoclinic, hardness 5 to 5.5, density 3.48 to 3.60, indices 1.843 to 2.110, above a refractometer’s limit.
Titanite is calcium titanium silicate, CaTiO(SiO4) on the IMA list: monoclinic, hardness 5 to 5.5, density 3.48 to 3.60. Its lowest refractive index on the Handbook sheet, 1.843, lies above the 1.81 limit of most refractometers, so a stone that gives a reading is not titanite. A 20.00 g piece reads 14.25 to 14.44 g in water.
In short
- The formula. The September 2026 IMA-CNMNC Master List lists titanite as CaTiO(SiO4), status A, 1967 s.p., Germany; the Handbook of Mineralogy sheet writes CaTiSiO5, the same atoms. Worked on standard atomic weights: 40.74% TiO2. The sheet’s Goschener Alp, Switzerland analysis prints 39.43%.
- The over-the-limit rule. The sheet’s indices run from α 1.843 to γ 2.110. The International Gem Society says titanite’s indices exceed 1.81, beyond most refractometer liquids, so readings are over the limit. Any stone that gives a reading on the scale is not titanite.
- Over the limit is not an identification. Andradite (1.887), zircon (1.925 and up) and diamond (2.4175) are over the limit too, on their sheets. Weight sorts most of them: titanite reads 14.25 to 14.44 g in water for 20.00 g, andradite 14.74 to 14.87 g, zircon 15.65 to 15.74 g. The gem society gives titanite a birefringence of 0.100 to 0.192, enough to double facet edges.
- Where the balance fails, documented. Diamond, at 3.511 on its sheet, reads 14.30 g, inside titanite’s window; it is isotropic and hardness 10. Hessonite, at 3.4 to 3.71 (gem society), reads 14.12 to 14.61 g and contains titanite’s whole window, and the gem society records grossular garnets and zircons misidentified as titanite. Hessonite gives a reading on the scale.
- Radioactivity: not on the sheet. The titanite sheet says it may be metamict and prints no radioactivity statement; a script finds 0 matches for radioac on it, against 1 on the zircon sheet, the control. This page draws no inference; the general question is on is my mineral radioactive, which is not advice.
| Material, source | Optical class | Refractive index | On a standard refractometer (limit about 1.81, IGS) | Hardness | 20.00 g piece in water | Separated from titanite by |
|---|---|---|---|---|---|---|
| Titanite, Handbook sheet | Biaxial (+) | α 1.843 to γ 2.110 | Over the limit | 5 to 5.5 | 14.25 to 14.44 g | - |
| Titanite, IGS | Biaxial (+); birefringence 0.100 to 0.192 | Exceeds 1.81 | Over the limit | 5 to 5.5 | 14.20 to 14.37 g (3.45 to 3.55) | - |
| Andradite, Handbook sheet | Isotropic; typically weakly anisotropic | 1.887 | Over the limit | 6.5 to 7 | 14.74 to 14.87 g | Weight, 0.30 g; single refraction |
| Demantoid (andradite), IGS | Isotropic; may show anomalous birefringence | 1.881 to 1.888 | Over the limit | Not used here | 14.76 to 14.85 g (3.82 to 3.88) | Weight; single refraction |
| Zircon, Handbook sheet | Uniaxial (+); isotropic when metamict | ω 1.925 to ε 2.015 | Over the limit | 7.5 | 15.65 to 15.74 g | Weight, at least 1.21 g |
| Zircon, GIA (low to high types) | Birefringence 0.000 to 0.059 | 1.810 to 1.984 (± up to 0.040) | Low type near the limit | 6 to 7.5 | 14.87 to 15.77 g (3.90 to 4.73) | Weight, at least 0.43 g |
| Diamond, Handbook sheet | Isotropic | 2.4175 (589 nm) | Over the limit | 10 | 14.30 to 14.31 g | Not weight: inside the window. Single refraction, hardness |
| Hessonite (grossular), IGS | Isotropic; may show anomalous birefringence | 1.730 to 1.757 | Reads on the scale | Not used here | 14.12 to 14.61 g | Not weight: contains the window. The refractometer |
| Cubic zirconia, IGS | Lacks titanite’s birefringence | Not given | Not given | Harder than titanite | Not given | Single refraction; IGS says it fluoresces and titanite does not |
What is titanite? Calcium titanium silicate
Titanite is calcium titanium silicate, CaTiO(SiO4), listed by the IMA as status A, 1967 s.p., the list’s mark for a special procedure that year. The September 2026 IMA-CNMNC Master List gives Germany as the country. The Handbook of Mineralogy sheet writes CaTiSiO5. On standard atomic weights the formula mass is 196.03 and the composition 28.61% CaO, 40.74% TiO2 and 30.65% SiO2, or 24.42% titanium. The sheet’s Goschener Alp, Switzerland analysis prints 28.57, 39.43 and 30.61, which the sheet gives as Ca1.00(Ti0.97Fe3+0.03)Si1.00O4.96.
What the sheet records. Monoclinic, point group 2/m, and it may be metamict. Crystals wedge-shaped, flattened parallel to {001} or prismatic along [110], to 16 cm; also compact and massive. Twinned on {100} by contact and penetration, less commonly lamellar on {221}. Cleavage good on {110}, with parting on {221} due to twinning. Hardness 5 to 5.5; density 3.48 to 3.60. Black, brown, grey, colourless, green, yellow or red; streak white; adamantine to resinous lustre.
Optics as printed. Biaxial (+), α 1.843 to 1.950, β 1.870 to 2.034, γ 1.943 to 2.110, 2V 17° to 40°, Z∧c = 51°, with strong r > v dispersion. Pleochroism is distinct when the crystal is deeply coloured: X nearly colourless, Y yellow to green, Z red to yellow-orange.
Can a refractometer read titanite? The over-the-limit rule
The over-the-limit rule: titanite’s lowest index is 1.843, above the roughly 1.81 limit of a standard refractometer, so any stone that gives a reading on the scale is not titanite. The International Gem Society says titanite’s refractive indices exceed 1.81 and that its readings will be over the limit, since that exceeds the index of most commercial contact liquids. The Handbook sheet’s α starts 0.033 above that figure.
What the rule clears. Most yellow, green and brown faceted stones read on the scale: on their sheets quartz reads 1.544 to 1.553, danburite 1.627 to 1.639, topaz 1.606 to 1.644, forsterite 1.635 to 1.670, and grossular 1.734. Each of those gives a shadow edge; titanite gives none.
What it does not clear. An over-the-limit result says only that the stone is above about 1.81. Andradite at 1.887, zircon at 1.925 and up, and diamond at 2.4175 do the same on their sheets. The gem society adds that titanite’s high birefringence, 0.100 to 0.192, usually doubles facet edges seen through the stone, much as in zircon or peridot; isotropic andradite and diamond do not double.
Titanite, zircon, demantoid or diamond? Weighing after the refractometer
Once a stone is over the limit, a balance separates titanite from andradite and zircon but not from diamond. Worked as 20 − 20/D for 20.00 g: titanite 14.25 to 14.44 g on its sheet; andradite 14.74 to 14.87 g, at least 0.30 g heavier; zircon 15.65 to 15.74 g on its sheet. GIA’s zircon facts give specific gravity down to 3.90 for low, radiation-damaged zircon, 14.87 g, still 0.43 g above titanite. The method is on how to measure specific gravity at home.
The diamond trap, a documented failure. The diamond sheet prints density 3.511 measured and 3.515 calculated: 14.30 and 14.31 g in water, inside titanite’s 14.25 to 14.44 g. Weight cannot separate them. Single against double refraction can, and so can hardness, 10 against 5 to 5.5, which is a test for rough only: how to test mineral hardness properly. The zircon question is on is zircon a diamond, whose own assets are not repeated.
The hessonite trap. The International Gem Society says brownish red to orange gems such as grossular garnets, zircons and rare bastnäsites have been misidentified as titanite, and vice versa. Hessonite, the orange grossular, reads 14.12 to 14.61 g on the gem society’s figures, a window that contains titanite’s whole range. Here the refractometer decides: hessonite reads 1.730 to 1.757 on the scale. The reasoning is on is hessonite a garnet.
Is titanite radioactive? What the sheet does and does not say
The Handbook titanite sheet prints no radioactivity statement; it says only that titanite may be metamict. A script finds 0 matches for radioac and 1 for metamict on the titanite sheet; on the zircon sheet, the control, it finds radioactive when metamict. This page does not infer radioactivity from the word metamict, because the sheet does not.
What the analyses show. The sheet’s second analysis, from New York (printed Pierceville [sic]), carries 1.22% rare-earth oxides and 1.0% Nb2O5 alongside 4.93% Al2O3 and 2.27% fluorine; its TiO2, 30.39%, is 74.59% of the ideal 40.74%. The sheet gives no uranium or thorium figure for either analysis.
Where to go. Whether any particular specimen is radioactive is a measurement, not a species fact, and the general method is on is my mineral radioactive. That page is general information and this is not safety advice.
Malayaite, vanadomalayaite and the high-aluminium titanites
Three IMA rows have the formula pattern CaMO(SiO4) with one element at M: titanite (Ti), malayaite (Sn) and vanadomalayaite (V). Method: the September 2026 list was parsed into 5,911 name and formula pairs and the formulas matched against Ca, one element, O(SiO4). Malayaite is A, 1964-024, Malaysia; vanadomalayaite A, 1993-032, Italy. Widening the pattern to any formula ending O(SiO4) adds three sodium rows, natisite, paranatisite and natrotitanite.
Malayaite on its sheet. Monoclinic with wedge-shaped crystals up to 3 cm, like titanite, but hardness 3.5 to 4, density 4.3 (15.35 g in water for 20.00 g) and indices α 1.764 to γ 1.801, on the refractometer’s scale. Its sheet prints that it fluoresces pale to bright yellow or yellow-green; the titanite sheet prints no luminescence, by a ligature-aware search.
Aluminium inside titanite. The sheet gives the New York analysis as (Ti0.74Al0.19Fe3+0.07) at the titanium site, with 0.23 fluorine: titanium still dominates, so it is still titanite. Its sheet reference is Oberti and others (1991) on the crystal chemistry of high-aluminium titanites.
What the name means, and where titanite is found
The name. The sheet derives titanite from titanium in its composition. The International Gem Society says mineralogists officially use titanite and many gemmologists use sphene, from the Greek for wedge, after the wedge-shaped crystals. A whole-line scan of the September 2026 IMA list finds 0 lines containing that gemmological name, so the species on such a label is titanite.
The Distribution field names fine specimens from Tavetsch, Graubünden, St. Gotthard, Ticino, and Zermatt, Valais, Switzerland; Val Maggia and St. Marcel, Val d’Aosta, Italy; the Schwartzenstein and Rothenkopf Mountains, Zillertal, Tirol, Austria; Arendal, Norway; Nordmark, Värmland, Sweden; the Lovozero and Khibiny massifs, Kola Peninsula, and large crystals from the Dodo mine in the Subpolar Urals, Russia; the Tilly Foster mine, Brewster, and Diana, Natural Bridge and Monroe, New York; Eganville and Turner’s Island, Ontario, and Litchfield, Quebec; El Rodeo, La Huerta and Piño Solo, Baja California, Mexico; Campo do Boa, Capelinha, Minas Gerais, Brazil; and Naevatanana and Ambalavaokely, Madagascar.
Cross-checked. The gem society’s Baja California, Zillertal and Capelinha agree with the sheet; its other gem countries are not on it and are not added. It occurs as an accessory mineral in intermediate and felsic plutonic rocks, pegmatites and alpine veins, with albite, epidote, apatite, magnetite and diopside among its associates. 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.