Csarite is the current proprietary trade name for gem-quality diaspore (aluminium oxide hydroxide, AlO(OH)) mined exclusively in the Ilbir Mountains of Muğla Province in south-western Turkey. Previously marketed under the name Zultanite, the stone was rebranded as Csarite in 2017 following a change in mine ownership. It remains the only commercially exploited deposit of facetable diaspore in the world, and its combination of a genuine colour-change phenomenon, single-source provenance, and the cutting challenges posed by its perfect cleavage have together established it as one of the more distinctive collector gemstones to enter the market in recent decades.

Mineralogy and Physical Properties

Diaspore belongs to the orthorhombic crystal system and is a hydroxide mineral — specifically an aluminium oxyhydroxide — closely related structurally to goethite and boehmite. Its chemical formula is AlO(OH), and it forms as a metamorphic mineral in bauxite deposits and aluminium-rich schists. The Ilbir Mountain deposit occurs within a metamorphic complex where diaspore crystallised in association with emery (a natural corundum–magnetite–spinel aggregate), a geological context that has long made Turkey significant in the world of industrial abrasives.

• Hardness: 6.5–7 on the Mohs scale
• Cleavage: Perfect in one direction {010}, making the stone highly susceptible to splitting during cutting and wear
• Specific gravity: approximately 3.35–3.40
• Refractive indices: approximately 1.702–1.750 (biaxial positive, high birefringence of ~0.048)
• Crystal system: Orthorhombic
• Lustre: Vitreous to pearly on cleavage surfaces

The high birefringence is optically significant: under magnification, doubling of back facets is visible, a characteristic that assists identification. The perfect cleavage is the stone's principal vulnerability, and lapidaries working with Csarite must orient the table facet carefully to minimise the risk of cleavage-related fracture both during cutting and in the finished stone.

Colour Change and Optical Behaviour

The defining characteristic of gem-quality Csarite is its pronounced colour change across different lighting conditions — a property that places it in the same commercially valued category as alexandrite and certain garnets, though its mechanism and colour palette are distinct. Under daylight or daylight-equivalent fluorescent illumination, the stone typically displays a kiwi green, sage green, or champagne-to-golden-yellow hue. Under incandescent or candlelight, the same stone shifts toward raspberry pink, purplish-pink, or a warm cognac. Intermediate lighting conditions — such as mixed indoor light — can produce a complex khaki or olive tone.

The colour change arises from the transmission characteristics of trace chromophores (principally manganese and, to a lesser extent, iron) within the crystal lattice, which interact differently with the spectral distributions of daylight versus tungsten illumination. The shift is genuine and repeatable, not a surface effect, and in fine specimens it can be dramatic enough to make the stone appear to be an entirely different gem under the two light sources.

Colour saturation varies considerably across the production. The most commercially desirable stones show a vivid, clean green in daylight and a strong raspberry or pinkish-purple under incandescent light. Paler, more washed-out examples — which are far more common — command considerably lower prices. A small proportion of production exhibits a brownish or olive cast that reduces desirability.

Origin and Mining

The Ilbir Mountains deposit, situated near the town of Milas in Muğla Province, is the sole known commercial source of gem-quality diaspore. The region has been mined industrially for emery for well over a century, but the gem potential of the associated diaspore crystals was not commercially developed until the early 2000s, when the stone was first introduced to the international market under the Zultanite trade name.

Mining is conducted at high altitude under challenging conditions. Gem-quality crystals occur as tabular to prismatic forms within the metamorphic host rock, and recovery of clean, unbroken material of significant size is inherently difficult given the mineral's perfect cleavage. The mine is operated under a controlled, single-source model, meaning that all Csarite on the market originates from one company's production — a structure that has allowed the brand to maintain consistent quality standards and provenance documentation, though it also means supply can be constrained.

Cutting and Fashioning

Cutting diaspore is considered one of the more demanding tasks in coloured-stone lapidary work. The perfect cleavage means that any misdirected blow, excessive vibration, or poorly oriented facet junction can split the rough irreparably. Experienced cutters orient the stone so that the cleavage plane runs parallel to the girdle where possible, reducing the risk of catastrophic fracture. Even so, yield from rough to finished stone is typically low.

Csarite is most commonly fashioned in oval, cushion, and pear shapes, which distribute stress more evenly than step cuts with their large flat facets. Brilliant-style cuts maximise the play of colour change and the stone's natural dispersion. Calibrated sizes are available but the stone's rarity in large clean pieces means that fine specimens above 5 carats are uncommon and command significant premiums. Stones above 10 carats are genuinely rare and attract collector-level interest.

Trade Names and Branding

The stone was introduced to the international gem trade in the early 2000s as Zultanite, a name evoking the Ottoman sultans who historically ruled the region of its origin. In 2017, following a change in mine ownership, the trade name was changed to Csarite. Both names refer to the same material — gem-quality diaspore from the Ilbir Mountains — and both remain in circulation in the trade, with older inventory and some dealers continuing to use Zultanite. The mineralogical species name, diaspore, is the scientifically correct designation and is used by gemmological laboratories in their reports regardless of which trade name the seller applies.

The single-source, branded model is unusual in the coloured-gemstone trade and draws comparison with Tanzanite (a single-mine tanzanite from the Merelani Hills) and Paraíba tourmaline (though the latter has since been found in multiple countries). The branding strategy has helped Csarite maintain a distinct market identity, though it has also meant that the stone's commercial profile is closely tied to the fortunes of one mining operation.

Treatments and Enhancements

Csarite is not known to be routinely treated. The stone is typically sold in its natural, untreated state, and no heat treatment, irradiation, or filling process has been documented as standard practice for this material. This absence of routine treatment is considered a positive attribute by the trade and by collectors. Gemmological laboratory reports for significant stones generally confirm no indications of treatment.

Identification and Laboratory Testing

Csarite can be distinguished from other colour-change stones by its combination of optical properties: the high birefringence (producing visible doubling of inclusions and back facets under magnification), its specific refractive index range, its orthorhombic optic character (biaxial positive), and its specific gravity. Colour-change garnets, which are the most commonly confused stones in the trade, are isotropic (singly refractive) and show no doubling. Alexandrite (colour-change chrysoberyl) has a higher hardness (8.5) and a different RI range. Spectroscopic examination and, where necessary, X-ray fluorescence or EDXRF analysis can confirm identity with certainty. Major gemmological laboratories including GIA issue identification reports for Csarite/diaspore.

Market and Collector Context

Csarite occupies a niche but genuine position in the collector and fine jewellery market. Its appeal rests on several factors: true single-source provenance, a dramatic and well-documented colour change, no routine treatments, and relative rarity in clean sizes above 5 carats. These attributes have attracted interest from collectors who value stones with a clear narrative and verifiable origin.

Pricing is strongly influenced by size, colour saturation, and the intensity of the colour change. Small, pale stones are relatively affordable; fine stones in the 5–10 carat range with vivid colour change command prices that reflect their scarcity. The stone has been used in high-end jewellery by independent designers and has appeared in auction catalogues, though it has not yet achieved the auction prominence of alexandrite or fine Paraíba tourmaline.

The stone's principal practical limitation for jewellery use is its cleavage: settings should protect the stone from lateral impact, and it is not ideally suited to rings worn daily. Pendants, earrings, and brooches are more appropriate applications for fine specimens.

Further Reading

• GIA Gems & Gemology — Diaspore from Turkey
• GIA Gem Encyclopedia: Diaspore