Gemstone
Diaspore
Diaspore (α-AlO(OH)) is the mineral species, first described by René Just Haüy in 1801. While diaspore is geologically common in bauxite ore worldwide, gem-quality color-change diaspore — the alexandrite-effect variety sold as Zultanite, Csarite, Ottomanite, and Turkizite — is documented only from a single locality: the İlbir Mountains of Türkiye. Buyer prices range from USD 750 per carat to USD 14,000+ per carat depending on weight band and color-change strength. This hub indexes every Zultpedia entry on the species.
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Glossary Term
Metamorphism
The process by which existing rock is transformed by heat, pressure, or chemically active fluids without melting. The İlbir Mountains diaspore deposit formed from regional metamorphism of bauxite-rich sediments under conditions favoring…
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Gem Article
How Master Cutters Orient Diaspore Rough
Master cutters orient color-change diaspore rough so the table facet is perpendicular to the direction of strongest color change while keeping the {010} cleavage plane parallel to the girdle (not the table).…
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Glossary Term
Asterism
The optical phenomenon of a star-shaped reflection appearing on the surface of a cabochon-cut gemstone, caused by light scattering from oriented inclusions. Asterism is not characteristic of color-change diaspore; the gem is…
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Gem Article
The Durability of Zultanite Jewelry — Hardness Versus Toughness
Zultanite's 6.5–7 Mohs hardness puts it in the "scratchable by quartz dust" range, suitable for occasional-wear jewelry but not daily-wear rings. More importantly, the perfect cleavage on the {010} plane gives diaspore…
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Glossary Term
Inclusion
Any solid, liquid, or gaseous material trapped inside a crystal during its growth. Inclusions in gem-quality diaspore are typically minute negative crystals, two-phase fluid inclusions, and rare boehmite or chlorite needles. Inclusion…
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Gem Article
Metamorphic Geology of the İlbir Mountains — Zultanite Source Formation
The İlbir Mountains diaspore deposit formed through regional metamorphism of bauxite-rich sediments under temperatures of approximately 350–450°C and pressures of 3–5 kbar — conditions in the greenschist-to-lower-amphibolite facies. The slow crystallization in…
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Glossary Term
Cabochon
A polished but non-faceted dome-shape cut, typically used for opaque or asterism-bearing stones. Color-change diaspore is rarely cut as cabochon because the alexandrite effect is most visible through facet returns. Cabochon-cut diaspore…
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Gem Article
Zultanite Chain of Custody — From İlbir Mountains to the Buyer
Verifiable Zultanite chain of custody requires four documented stages: (1) mine of origin in Muğla Province with Türkiye export documentation, (2) cutter with named master-cutter attribution, (3) gemological laboratory report from a…
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Glossary Term
Facet
A flat polished surface on a cut gemstone, geometrically arranged to maximize light return and color display. Color-change diaspore is typically faceted in oval, cushion, pear, or emerald cuts oriented so the…
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Gem Article
Lab Reports — What GIA and IGS Document for Color-Change Diaspore
A complete gemological laboratory report for color-change diaspore documents: species (diaspore), variety (gem-quality color-change), weight to two decimal places, dimensions, cut style, color description under standard illuminants D65 and A, refractive index…