Key properties
| Chemical formula | Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4 |
| Crystal system | Tetragonal |
| Mohs hardness | 6.5 |
| Toughness | Fair (single crystals) to good (massive aggregates) |
| Refractive index | 1.713-1.718 |
| Birefringence | 0.0010-0.0120 |
| Optic character | Uniaxial positive or negative (highly variable); strong anomalous (strain) interference colours are typical (+/-) |
| Dispersion | 0.0190 |
| Specific gravity | 3.32-3.45 |
| Cleavage | Indistinct, rarely seen |
| Fracture | Conchoidal to uneven to granular |
| Habit | Prismatic, lengthwise-striated crystals; frequently massive columnar or compact aggregates |
| Lustre | Vitreous on crystals, greasy to dull on massive material; polish: Vitreous to greasy |
| UV fluorescence | Inert |
| Pleochroism | None to weak |
| Cause of colour | Iron colours the common green, yellow and brown stones; copper produces the rare blue cyprine; manganese-rich xanthite tends yellow-brown. |
| Typical inclusions | Strong parallel striations, liquid veils; the jade-like californite is typically intergrown with hydrogrossular garnet |
| Stability | Fuses easily under a torch; stable to light; attacked by hydrochloric acid |
| Heat sensitivity | High - fuses readily |
| Care and cleaning | Warm soapy water safe; ultrasonic and steam risky |
| Availability | Limited; californite occasional, transparent gems scarce |
| Recognition | Spot RI about 1.71 with an aggregate or strained uniaxial reaction, SG near 3.4, a 464 nm spectrum line, and greasy lustre on massive material point to idocrase. |
Varieties (4)
Californite (Green Idocrase)
| Colour | green to yellowish or brownish green, often mottled or veined white |
| Transparency | translucent to opaque |
| Clarity type | Ornamental aggregate - judged on colour and structure |
| Phenomena | None |
| Appearance | Compact jade-like green to yellow-green material, frequently mottled or veined in white and grey; takes a waxy-greasy polish reminiscent of nephrite. |
| Trade names | californite • idocrase jade |
| Misnomers | California jade • American jade • vesuvianite jade |
| Typical sizes | Large pieces available; cabochons of virtually any size |
| Cutting styles | Cabochons, carvings, beads; occasionally faceted in translucent slabs |
| Key separations | vs nephrite: nephrite SG 2.95 and RI about 1.62 vs californite 3.4/1.71; vs jadeite: jadeite RI 1.66, SG 3.33 and fibrous texture; vs hydrogrossular: properties overlap so far that mixed material can be inseparable without RI/spectrum/SG work - 50-50 intergrowths genuinely occur |
| Sources (localities) | USA (California - name source; also Pakistan) • Italy • Canada • Norway |
| Availability | Limited; specialist dealers and carving suppliers |
| Market notes | Inexpensive ornamental; sells on jade-like look without jade price |
| Care notes | Warm soapy water; ultrasonic and steam risky; keep from acids and torch heat |
| In short | Californite is the jade-like green idocrase-hydrogrossular aggregate from California sold as 'California jade'. Higher RI and SG than true jade give it away; its low price and soft polish keep it popular for carvings. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $12.00 | commercial ornamental | 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.
Yellow-Brown Idocrase
| Colour | yellow, golden to brownish yellow and greenish brown |
| Transparency | transparent to translucent |
| Clarity type | Type II (typically included) |
| Phenomena | None |
| Appearance | Warm golden to olive-brown transparent gems with a bright, almost demantoid-like sparkle from the high dispersion; colours echo prehnite or hyacinth zircon. |
| Trade names | xanthite (yellow-brown manganese-rich type) • idocrase |
| Misnomers | occasionally confused with calderite or hessonite at sight - always test |
| Typical sizes | 1 to 10 ct |
| Cutting styles | Faceted in mixed cuts; some carved |
| Key separations | vs hessonite grossular: hessonite is SR isotropic with roiled 'treacle' inclusions; vs sphene: sphene RI 1.84-1.90 with much higher lustre; vs chrysoberyl: RI 1.74-1.75 and SG 3.7; the 464 nm line plus anomalous strain colours are idocrase signatures |
| Sources (localities) | Italy (Ala Valley) • Switzerland (Zermatt) • Canada (Quebec) • Norway • Russia (Wilui) • Pakistan • USA (Maine, New Hampshire) |
| Availability | Scarce; collector and specialist trade |
| Market notes | Modest value; strong dispersion gives lively stones an appeal beyond their price |
| Care notes | Warm soapy water; ultrasonic and steam risky; fuses under torch heat |
| In short | Transparent golden-brown idocrase is a bright, dispersive collector gem of modest price. The 464 nm line and anomalous interference colours clinch the identification. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–5.00 | $20.00 – $80.00 | collector | 2026-10-26 |
| 5.00–10.00 | $30.00 – $120.00 | collector to fine | 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.
White-Grey Idocrase
| Colour | white to grey massive |
| Transparency | translucent to opaque |
| Clarity type | Ornamental aggregate |
| Phenomena | None |
| Appearance | Chalky white to pale grey compact material, usually veined; of minor ornamental interest. |
| Trade names | white idocrase |
| Misnomers | sometimes sold as 'white jade' simulants - test before using the word jade |
| Typical sizes | Large slabs and cabochons |
| Cutting styles | Cabochons, carvings, inlay |
| Key separations | vs howlite/magnesite: both are much softer and effervesce or absorb water differently; vs white jadeite: jadeite RI 1.66, SG 3.33 |
| Sources (localities) | Same districts as green idocrase: Italy • Canada • USA |
| Availability | Rare in trade |
| Market notes | Negligible value; mostly a lapidary curiosity |
| Care notes | Warm soapy water |
| In short | White-grey idocrase is a minor ornamental aggregate, mostly seen as veining within californite. Spot RI about 1.71 separates it from common white lookalikes. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $8.00 | ornamental | 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.
Grey-Black Idocrase
| Colour | grey to nearly black |
| Transparency | opaque |
| Clarity type | Ornamental aggregate |
| Phenomena | None |
| Appearance | Deep slate-grey to black compact idocrase with a greasy sub-vitreous polish; occasional bronze flashes from included mica. |
| Trade names | black idocrase |
| Misnomers | should not be sold as 'black jade' |
| Typical sizes | Cabochons and small carvings |
| Cutting styles | Cabochons, carvings |
| Key separations | vs black nephrite/jadeite: jade RI 1.62-1.66 and lower SG; vs black chalcedony: cryptocrystalline, no cleavage; vs basalt/glass: SG and RI differences |
| Sources (localities) | With other massive idocrase: Canada • Italy • USA |
| Availability | Rare |
| Market notes | Negligible; lapidary curiosity |
| Care notes | Warm soapy water; keep from acids and heat |
| In short | Grey-black idocrase is a rare, heavy opaque ornamental variant. Its high SG and spot RI 1.71 distinguish it from black jades and chalcedony. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–20.00 | $1.00 – $8.00 | ornamental | 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
· 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 #86 · gem #110 · gem #126 · gem #180 · gem #200
Related materials: Corundum · Diamond · Opal · Quartz · Spinel · Topaz
Identification wizard · All 83 materials · Singapore gem labs