Key properties
| Chemical formula | (Ca,Na)(Al,Si)4O8 (50-70 percent anorthite component) |
| Crystal system | Triclinic |
| Mohs hardness | 6-6.5 |
| Toughness | Poor to fair (cleavage and parting prone) |
| Refractive index | 1.559-1.568 |
| Birefringence | 0.0070-0.0100 |
| Optic character | Biaxial positive (+) |
| Specific gravity | 2.65-2.75 |
| Cleavage | Perfect and easy in two directions near 90 degrees; parting common |
| Fracture | Uneven to splintery |
| Habit | Tabular, often striated crystals; frequently massive (blocky aggregate) for ornamental use |
| Lustre | Vitreous, pearly on cleavages; polish: Vitreous |
| UV fluorescence | Usually inert; some weak patchy white in long- and short-wave UV. |
| Pleochroism | Usually none; yellow material may show colourless to light yellow dichroism. |
| Cause of colour | Body colours are grey to near black from fine inclusions and structural iron; the celebrated labradorescence is thin-film interference from sub-micron exsolution lamellae (Boeggild intergrowth, roughly 128-252 nm spacing) within the calcic feldspar. |
| Typical inclusions | Fine polysynthetic (repeated) twinning striations; black needle-like ilmenite inclusions; reflective copper or hematite platelets in sunstone labradorite |
| Stability | Stable to light; heat can crack or cleave; attacked rapidly by hydrofluoric acid and slowly by hydrochloric acid |
| Heat sensitivity | May crack or cleave with heat |
| Care and cleaning | Warm soapy water only; never ultrasonic or steam |
| Availability | Plentiful for phenomenal (labradorescent) material; transparent and cat's-eye material limited |
| Recognition | One glance at the multicolour flash plus spot RI 1.56 and two cleavages identifies labradorite; repeated twin striations under magnification confirm it. |
Varieties (2)
Labradorite (spectrolite)
| Colour | dark grey to near black body with vivid blue, gold, green and sometimes red labradorescent flashes |
| Transparency | variable (translucent to opaque) |
| Clarity type | Phenomenal ornamental material judged on flash, not internal clarity |
| Phenomena | Labradorescence • rare aventurescence, chatoyancy and asterism |
| Appearance | A sooty grey feldspar that erupts into neon blue, peacock green and gold sheets of light when rotated; the best Finnish spectrolite shows a full rainbow of flashes across a single face. |
| Trade names | spectrolite (registered name for fine Finnish labradorite from Ylaemaa) • rainbow labradorite |
| Misnomers | 'black moonstone' (dark flash labradorite) • 'labrador moonstone' |
| Typical sizes | Cabochons from 1 ct to very large ornamental slabs; faceted stones to about 100 ct known |
| Cutting styles | Cabochons oriented to place the flash on the dome; also carved into decorative objects and beads |
| Key separations | vs rainbow obsidian: obsidian is natural glass (SR, conchoidal, SG 2.4); vs flash glass imitations: glass is singly refractive with swirls and bubbles; vs dark nephrite or basalt carvings: RI, hardness and SG |
| Sources (localities) | Madagascar (main volume) • Finland (Ylaemaa spectrolite) • Canada (Nain, Labrador - type area) • Russia • China • Norway • Australia • Ukraine |
| Availability | Plentiful in commercial grades; fine spectrolite limited |
| Market notes | Very affordable in calibrated cabochons; fine Finnish spectrolite commands premiums; also widely used in carving and decorative facing stone |
| Care notes | Warm soapy water; no ultrasonic or steam; cleavages can chip in thin carvings |
| In short | Labradorite's dark body lit by rolling blue-gold interference flashes is one of the most recognisable gems in the trade. Madagascar supplies most material, Finland the finest spectrolite. Durable enough for pendants and beads but too cleavage-prone for rough wear. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–10.00 | $2.00 – $12.00 | commercial | 2026-10-26 |
| 10.00–50.00 | $5.00 – $60.00 | fine (spectrolite-grade flash) | 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.
Transparent Labradorite
| Colour | colourless to water-white, often with a blue or multicolour flash |
| Transparency | transparent |
| Clarity type | Type II (typically included) |
| Phenomena | Labradorescence (blue flash in 'rainbow moonstone') • rare cat's-eye |
| Appearance | Glassy, water-clear feldspar whose better grades glow with a rolling blue or multicolour sheen just below the surface - the trade's 'rainbow moonstone'. |
| Trade names | rainbow moonstone • transparent labradorite |
| Misnomers | 'rainbow moonstone' - it is labradorite, not true (orthoclase) moonstone |
| Typical sizes | 1 to 20 ct; faceted stones to about 100 ct known |
| Cutting styles | Faceted when clean; cabochons when flash-bearing |
| Key separations | vs orthoclase moonstone: rainbow moonstone is transparent with multicolour flash and RI 1.559-1.568 vs 1.518-1.526; vs rock crystal quartz: quartz is uniaxial with RI 1.544-1.553 and no cleavage; vs beryl: beryl is uniaxial with RI 1.57-1.59 |
| Sources (localities) | Madagascar (main for rainbow moonstone) • Mexico • Oregon USA (transparent copper-bearing sunstone labradorite) |
| Availability | Limited but steady for rainbow moonstone; Oregon sunstone a specialist trade |
| Market notes | Rainbow moonstone undercuts fine blue orthoclase moonstone in price; Oregon copper-bearing labradorite is a premium American product usually sold as sunstone |
| Care notes | Warm soapy water; no ultrasonic or steam |
| In short | Transparent labradorite ranges from water-clear facet rough to the blue-flashing 'rainbow moonstone' of the trade, chiefly from Madagascar. Higher RI and SG quickly separate it from true moonstone. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–10.00 | $5.00 – $30.00 | commercial to fine | 2026-10-26 |
| 10.00–30.00 | $10.00 – $80.00 | fine to collector (Oregon copper-bearing) | 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 #116 · gem #169 · gem #209
Related materials: Oligoclase Feldspar
Identification wizard · All 83 materials · Singapore gem labs