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
Refractive Index
The ratio of the speed of light in a vacuum to the speed of light in a given material. In gemology, refractive index is one of the primary identification tools, measured on…
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Glossary Term
Specific Gravity
The ratio of a substance's density to the density of water at 4°C. For gemstones, specific gravity is a primary identification tool measured by hydrostatic weighing or heavy-liquid suspension. Diaspore has a…
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Glossary Term
Illuminant
A specified light source used to evaluate gemstone color, defined by its color temperature in Kelvin and its spectral power distribution. Standard illuminants in gemology include D65 (average daylight, 6500 K), A…
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Glossary Term
Birefringence
The difference between the highest and lowest refractive indices of an anisotropic gemstone. High birefringence produces visible doubling of pavilion facet edges when the gem is examined through the table. Diaspore has…
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Property Guide
Hardness of Zultanite — 6.5 to 7 on the Mohs Scale
Zultanite (gem-quality color-change diaspore) measures 6.5 to 7 on the Mohs hardness scale, comparable to peridot and below quartz. This places it in the moderately hard range — durable enough for pendants,…
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Property Guide
Refractive Index of Zultanite — 1.682 to 1.752
Zultanite (gem-quality color-change diaspore) has a refractive index range of 1.682 to 1.752 with strong birefringence (~0.048). It is a biaxial positive gem with three distinct refractive indices: nα 1.682–1.706, nβ 1.705–1.725,…
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Property Guide
Specific Gravity of Zultanite — 3.30 to 3.39
Zultanite (gem-quality color-change diaspore) has a specific gravity of approximately 3.30 to 3.39, depending on trace-element content. It is heavier than quartz (2.65) and tourmaline (3.06), comparable to topaz (3.49–3.57), and lighter…
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Property Guide
Color Change of Zultanite — Three Illuminants, One Crystal
Zultanite shifts visible color across three illuminants: sage-green under cool daylight (6500 K), champagne-gold under indoor incandescent or fluorescent light (~3000 K), and raspberry-pink under candlelight (~1850 K). The shift is caused…
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Property Guide
Pleochroism of Zultanite — Three Crystallographic Colors
Zultanite shows strong trichroic pleochroism: it displays three different colors when viewed along its three principal crystallographic axes. Typical pleochroic colors are kiwi-green, dark green-brown, and pinkish-orange. This is independent of the…
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Glossary Term
Alexandrite Effect
Alexandrite effect (also called color change) is the appearance of distinctly different colors in the same gemstone under different illuminants — typically daylight versus incandescent or candlelight. Named after the gemstone alexandrite,…