Reference
Zultanite Properties — Verified Mineralogy
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Property Guide
Cleavage of Zultanite — Perfect on {010}
Zultanite (gem-quality color-change diaspore) has perfect cleavage on the {010} crystallographic plane. This is the dominant durability constraint for the gem: a sharp impact aligned with that plane can cleave the stone…
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Property Guide
Toughness of Zultanite — Why Hardness Alone Lies
Zultanite's 6.5–7 Mohs hardness measures scratch resistance, not toughness. Toughness — resistance to chipping and cleaving under impact — is rated only "fair" for diaspore because of its perfect {010} cleavage. A…
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Property Guide
Crystal Habit of Diaspore — Tabular, Acicular, Massive
Diaspore commonly forms thin platy or tabular crystals flattened on {010}, occasionally elongated needle-like (acicular) crystals along the c-axis, and frequently as fine-grained massive aggregates within bauxite ore. Gem-quality crystals from the…
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Property Guide
Optical Character of Zultanite — Biaxial Positive
Zultanite is biaxial positive: light traveling through the crystal splits into two rays with three principal refractive indices (nα 1.682–1.706, nβ 1.705–1.725, nγ 1.730–1.752), with nβ closer to nα than to nγ.…
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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…