Key properties
| Chemical formula | Ca3Al2(SiO4)3-x(OH)4x |
| Crystal system | Cubic |
| Mohs hardness | 6.5-7 |
| Toughness | Good |
| Refractive index | 1.670-1.730 |
| Optic character | SR (singly refractive; isotropic) - aggregate reaction in massive material |
| Specific gravity | 3.15-3.55 |
| Cleavage | None |
| Fracture | Uneven, granular to splintery (massive material) |
| Habit | Massive, compact, sometimes intergrown with idocrase/vesuvianite |
| Lustre | Greasy to vitreous; polish: Vitreous to waxy |
| UV fluorescence | Inert |
| Pleochroism | None |
| Cause of colour | Green from chromium (with possible iron contribution); pink from manganese; white essentially pure |
| Typical inclusions | Black peppery chromite/spinel specks common in green South African material • mottled aggregate texture |
| Stability | Stable to light and normal chemicals; very slightly attacked by hydrofluoric acid |
| Heat sensitivity | Abrupt temperature change may cause fracturing |
| Care and cleaning | Ultrasonic usually safe • steamer risky • warm soapy water safe |
| Birthstones | January (garnet, by group membership) |
| Availability | Limited but steady for ornamental cabochon and bangle material |
| Recognition | Unfamiliar to most consumers; usually met as 'African jade' rather than by its own name |
Varieties
Hydrogrossular
| Colour | green to bluish green; also pink, white and grey |
| Transparency | opaque |
| Clarity type | N/A - translucent to opaque massive material |
| Phenomena | None |
| Appearance | A compact, waxy-to-greasy ornamental stone - green hydrogrossular looks like nephrite at a glance but with a slightly coarser, mottled texture and black peppery specks. |
| Trade names | South African jade • African jade |
| Misnomers | Transvaal jade • garnet jade |
| Typical sizes | Large pieces available; bangles, beads and big cabochons are the norm |
| Cutting styles | Cabochons • bangles • beads • carvings |
| Key separations | vs jadeite: jadeite RI 1.66, SG 3.30-3.36, poliscope aggregate, fibrous/interlocking texture; hydrogrossular spot RI up to 1.73 and SG range wider • vs nephrite: nephrite RI 1.62, SG 2.95, fibrous fracture • vs idocrase/californite: properties overlap almost completely - separation may be impossible by routine tests • vs prehnite: prehnrite lower RI (~1.62) • dyed material: concentrated colour in fractures |
| Sources (localities) | South Africa (Bushveld/Transvaal - green) • Myanmar (pink) • China (white to pale green) • Canada (British Columbia) • USA (California) • New Zealand |
| Availability | Limited but reliable supply of ornamental grades |
| Market notes | Marketed almost exclusively as a jade lookalike - sell it on its own merits as a tough natural garnet. Some material is dyed to deepen green. |
| Care notes | Wipe with damp cloth; mild soap for bangles; no steamer |
| In short | Hydrogrossular is the massive green, pink or white hydrated garnet sold as 'Transvaal jade'. Tough, carvable and inexpensive, it makes honest bangles and beads if labelled correctly. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $15.00 | ornamental | 2026-10-26 |
| 20.00–100.00 | $1.00 – $8.00 | carving rough / large cabs | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #198
Related materials: Almandine Garnet · Andradite Garnet · Grossular Garnet · Pyrope Garnet · Rhodolite Garnet · Spessartine Garnet · Tsavorite Garnet
Identification wizard · All 83 materials · Singapore gem labs