Topic
Mineralogy
Mineralogy entries on Zultpedia document the species-level identity of color-change diaspore: chemistry (α-AlO(OH)), crystal system (orthorhombic), refractive indices, pleochroism, perfect cleavage on {010}, and the trace iron + chromium chromophore mechanism that produces the alexandrite effect. Sourced from primary mineralogical literature (Mindat, Mineralogical Magazine, Wikipedia’s peer-reviewed mineral pages) and the Hatipoğlu et al. 2010 İlbir Mountains study.
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Gem Article
Pleochroism vs Color Change in Zultanite — Two Optical Effects, One Crystal
Pleochroism and color change are two distinct optical phenomena that both appear in diaspore. Pleochroism (different colors visible from different viewing angles in the same illuminant) is caused by the orthorhombic crystal's…
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Gem Article
Why Zultanite Has No Secondary Locality
Diaspore is geologically common — it occurs in every major bauxite deposit on Earth. Gem-quality color-change diaspore is not, because the simultaneous geological conditions required (slow metamorphic crystallization plus the specific iron-to-chromium…
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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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Gem Article
The Absorption Spectrum of Color-Change Diaspore
Color-change diaspore from the İlbir Mountains shows a characteristic UV-Vis-NIR absorption profile dominated by trace iron (Fe³⁺ band near 425 nm) and trace chromium (Cr³⁺-related broad absorption centered near 580 nm). Transmission…
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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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Glossary Term
Bauxite
A sedimentary rock composed primarily of three aluminum hydroxide minerals: gibbsite, böhmite, and diaspore. Bauxite is the world's primary aluminum ore. Most bauxite-hosted diaspore occurs as fine crystals of no gem interest.…
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Gem Article
The History of Color-Change Diaspore — From Haüy to the İlbir Mountains
Color-change diaspore — the mineral species — was first described by René Just Haüy in 1801 in the Mineralogie volume of his foundational works. Gem-quality material from the İlbir Mountains of southwestern…
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Education Article
How to Identify Zultanite — A Five-Step Field Guide
Identifying Zultanite (color-change diaspore) requires five tests: (1) check for color change between daylight and incandescent illuminants, (2) verify trichroic pleochroism with a dichroscope, (3) measure refractive index 1.682–1.752 with strong birefringence…
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Glossary Term
Cleavage
The tendency of a crystal to split along specific planes determined by its internal atomic structure. Cleavage quality is described as perfect, distinct, indistinct, or absent. Diaspore has perfect cleavage on the…
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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…
