Uvarovite
Uvarovite, Ca3Cr2(SiO4)3, is the calcium chromium garnet: hardness 6.5 to 7, density 3.77 to 3.81, index 1.865. How much of a real crystal is uvarovite.
Uvarovite is the calcium chromium garnet, Ca3Cr2(SiO4)3: cubic, hardness 6.5 to 7, density 3.77 to 3.81, refractive index 1.865. GIA says it usually forms crystals too small to cut. Worked on the sheet’s Outokumpu, Finland analysis, chromium fills 89.1% of the Y site and aluminium 9.5%: uvarovite carrying a grossular share.
In short
- One species of the garnet group. The September 2026 IMA-CNMNC Master List lists uvarovite as Ca3Cr2(SiO4)3, A, 1967 s.p., Russia. Grew et al., American Mineralogist 98 (2013) place it in the garnet group as {Ca3}[Cr3+2](Si3)O12. The Handbook of Mineralogy sheet names one series, with grossular. GIA calls it a green garnet that usually occurs as crystals too small to cut.
- The Outokumpu split. The sheet’s only analysed specimen, from Outokumpu, Finland, has Cr 1.79, Al 0.19 and Fe3+ 0.03 at the Y site: worked, 89.1% chromium, 9.5% aluminium, 1.5% iron. Its Cr2O3, 27.54%, is 90.7% of the ideal 30.37%. By the dominant-constituent rule Grew et al. apply, it is uvarovite; about a tenth of it is the grossular component.
- Documented failure: isotropic is not a rule. The sheet says weak anisotropism due to internal strain is typical. The International Gem Society says some uvarovites are birefringent and that monoclinic, orthorhombic and triclinic symmetry occurs in natural uvarovites; Grew et al. cite a structure refinement of birefringent uvarovite. GIA’s garnet facts give birefringence none.
- Two sets of numbers. The sheet gives n = 1.865 and density 3.77 to 3.81, 14.69 to 14.75 g in water for 20.00 g. The gem society gives 1.74 to 1.87 and 3.40 to 3.80, usually 3.71 to 3.77: down to 14.12 g. A light reading does not exclude uvarovite on the gem society’s figures.
- Is uvarovite radioactive? The uvarovite sheet prints nothing about radioactivity, by script, and its formula contains no uranium or thorium. For a specimen that reads on a counter, see is my mineral radioactive; that is not advice.
| Material | Y site (source) | Cr share of Y | Refractive index | Density; 20.00 g piece in water | Optical note |
|---|---|---|---|---|---|
| Uvarovite, Ca3Cr2(SiO4)3 | Cr2 (IMA; sheet) | 100% | 1.865 (sheet) | 3.77 to 3.81; 14.69 to 14.75 g | Weak strain anisotropism typical (sheet) |
| Outokumpu, Finland | Cr 1.79, Al 0.19, Fe3+ 0.03 (sheet analysis 1) | 89.1%, worked | - | - | - |
| Uvarovite, gem figures | Not stated | - | 1.74 to 1.87 (IGS) | 3.40 to 3.80, usually 3.71 to 3.77 (IGS); 14.12 to 14.74 g | Some truly birefringent (IGS) |
| Grossular, Ca3Al2(SiO4)3 | Al2: the series end (sheet) | 0% | 1.734 (sheet) | 3.594; 14.44 g | Weak strain birefringence (sheet) |
| Andradite, Ca3Fe3+2(SiO4)3 | Fe3+2 (IMA) | 0% | 1.887 (sheet) | 3.8 to 3.9; 14.74 to 14.87 g | Typically weakly anisotropic (sheet) |
| Knorringite, Mg3Cr2(SiO4)3 | Cr2, with Mg at X (IMA: A, 1968-010, Lesotho) | 100% | 1.803 (sheet) | 3.756; 14.68 g | Isotropic (sheet) |
| Garnet, all species | - | - | 1.714 to 1.888 (GIA) | 3.47 to 4.15 (GIA) | Birefringence none (GIA) |
What is uvarovite? The calcium chromium garnet
Uvarovite is the garnet with calcium at X and chromium at Y, Ca3Cr2(SiO4)3. The September 2026 IMA-CNMNC Master List gives it status A, 1967 s.p., Russia. On standard atomic weights the formula mass is 500.47, with 33.61% CaO, 30.37% Cr2O3 and 36.02% SiO2, the sheet’s ideal column to the second decimal; chromium is 20.78% of the mass. Grew et al., American Mineralogist 98 (2013) list it in the garnet group with the oldest description by Hess (1832).
What the sheet records. Cubic, point group 4/m -3 2/m; commonly euhedral dodecahedra or trapezohedra, or in combination with other cubic forms, to 4.5 cm; fine or coarse granular, compact or massive. Fracture uneven to conchoidal, brittle. Hardness 6.5 to 7; density 3.77 to 3.81, calculated 3.848. Emerald-green to dark green, may be sectored; streak white; vitreous. A ligature-aware search finds no fluorescence printed.
Usually a druse. GIA’s garnet description calls uvarovite a sixth gem garnet, after the five commercially important species, that usually occurs as crystals too small to cut and is sometimes set as clusters. The International Gem Society says it is usually only seen as druzy on matrix and that faceted pieces hardly ever exceed one carat. A druse on matrix cannot be weighed in water as uvarovite: the balance reads the matrix too. The method is on how to measure specific gravity at home.
How much of a real uvarovite is uvarovite? The Outokumpu split
The Outokumpu split: in the sheet’s analysed uvarovite, chromium fills 89.1% of the Y site, aluminium 9.5% and ferric iron 1.5%. The sheet prints the Outokumpu, Finland formula as (Ca2.88Mg0.06)(Cr1.79Al0.19Fe3+0.03)Si3.02O12. Recalculated from its oxides on 12 oxygens it gives Cr 1.790, Al 0.187, Fe 0.025, Ca 2.884 and Mg 0.061, matching the printed figures. Calcium is 98.0% of the X site.
Why it is still uvarovite. Grew et al., American Mineralogist 98 (2013) name garnet species by the dominant-valency and dominant-constituent rules: at Y all three cations are trivalent, and chromium dominates. Aluminium at Y is the grossular component; the sheet’s series with grossular is the line along which it would change name, at the point where aluminium overtakes chromium. Cr2O3 at 27.54% is 90.7% of the end-member’s 30.37%.
What the split does not tell you. One analysis is one crystal; the sheet gives no range across localities, and this page does not extend the figure to other Outokumpu material.
Is uvarovite isotropic? Where the garnet optics test fails
A documented failure: uvarovite is cubic on its sheet, yet the sheet says weak anisotropism due to internal strain is typical. The International Gem Society uvarovite article goes further: the large calcium atom may make some specimens birefringent, through strain or symmetry reduction, and monoclinic, orthorhombic and triclinic symmetry does occur in natural uvarovites. Grew et al.’s entry for uvarovite cites a structure refinement of birefringent uvarovite (Wildner and Andrut 2001).
The sources disagree on the garnet default. GIA’s garnet facts give birefringence none and refractive index 1.714 to 1.888. A polariscope showing anomalous extinction does not rule out uvarovite. Where the line between a birefringent garnet and a different mineral falls is on is vesuvianite a garnet.
The figures themselves differ. The sheet prints one index, 1.865, and 3.77 to 3.81; the gem society 1.74 to 1.87 and 3.40 to 3.80. Both are printed in the table above, and neither is preferred.
Uvarovite, chromite and the chromium garnets
Uvarovite grows where calcium meets chromite. The sheet’s Occurrence: from hydrothermal alteration of serpentinite containing chromite; in metamorphosed limestones and skarns from the reaction of dolomite and chromite. Its associates are chromite, diopside, zoisite, olivine, dolomite, tremolite, quartz, plagioclase, epidote, calcite, chromian clinochlore and pyroxenes. The chromite page’s chromium figures are not repeated here.
Two IMA rows have the shape X3Cr2(SiO4)3. A script over the September 2026 list finds uvarovite, Ca3Cr2(SiO4)3, and knorringite, Mg3Cr2(SiO4)3, A, 1968-010, Lesotho. The knorringite sheet gives n = 1.803 and density 3.756. The chromium pyrope series and the old label chrome garnet are decoded on pyrope.
Weight against andradite. At 14.69 to 14.75 g in water for 20.00 g, uvarovite overlaps andradite at 14.74 to 14.75 g; the index, 1.865 against 1.887, is 0.022 apart. The green grossular question is on is tsavorite a garnet.
Where uvarovite is found, and its name
The Distribution field: although an uncommon garnet, still with numerous localities. The Saranovskii mine, Biserskoye, Gorozavod district, and other localities around Yekaterinburg, Urals, Russia; exceptional crystals from Outokumpu, Finland; Pico do Posets, near Vénasque, Pyrenees, Spain; South Ham, Quebec; Wood’s Chrome mine, Pennsylvania; Riddle, Oregon; the Red Ledge mine, around Newcastle and near New Idria, California; Taiwan; Ergani Maden and the Kop Krom mine, near Aşkale, Turkey. The International Gem Society also names Afghanistan, Thetford, China, Norway and South Africa; they are not on the sheet and we add none.
Three accounts of one man. The sheet names Count Sergei Semenovich Uvarov (1786–1855), Russian nobleman and President of the Academy of Sciences; Grew et al. call him a Russian historian, 1786–1855; the gem society gives Count S. S. Uvarov, 1765–1855, mineral collector and president of the St. Petersburg Academy. The dates differ by 21 years at birth; all three are printed.
Related pages. The calcium aluminium garnet is grossular; 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.