Diaspore
Diaspore is aluminum oxide hydroxide, AlO(OH), a hard, dense mineral that forms in aluminum-rich metamorphic and hydrothermal environments and ranks among the principal minerals in bauxite ore. It is dimorphous with boehmite, sharing an identical chemical formula but a different crystal structure, and it characteristically splits apart with a sudden crackling sound when heated, a property that inspired its name. Transparent gem-quality crystals, sold as zultanite or csarite, display a striking color change from green to pink or champagne under different lighting.
Diaspore properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | AlO(OH) |
| Mohs hardness | 6.5–7 |
| Crystal system | Orthorhombic |
| Luster | Vitreous to pearly on cleavage |
| Streak | White |
| Cleavage | Perfect on {010} |
| Fracture | Conchoidal |
| Specific gravity | 3.3–3.5 |
| Transparency | Transparent to translucent |
| Common colors | Colorless, White, Gray, Yellowish, Brown, Green, Violet-pink (color-change) |
| Rarity | common |
Geology & background
Diaspore forms during the metamorphism of aluminum-rich rocks such as bauxite, emery, and some corundum-bearing deposits, where high-alumina conditions favor its crystallization over other aluminum hydroxide minerals. It is a significant component of bauxite deposits worldwide and also occurs as an accessory mineral in emery deposits on the Greek island of Naxos and in Turkey's Anatolia region. The color-change gem variety, marketed as zultanite, comes almost exclusively from the Ilbir Mountains in Turkey's Mugla Province.
Collectors of color-change gemstones seek diaspore for its dramatic shift from green or yellow-green in daylight to pink, raspberry, or champagne tones under incandescent light, a phenomenon caused by selective light absorption tied to trace chromium and iron. Because gem-quality crystals come from a single restricted Turkish source, prices for larger, clean stones have climbed steadily. Rockhounds working bauxite or emery deposits should note diaspore's tendency to occur as small, easily overlooked grains rather than large, obvious crystals.
How to identify Diaspore
Diaspore ranges from colorless and white to gray, yellowish, or greenish, with a vitreous to pearly luster on cleavage surfaces and a white streak. It is notably hard for an aluminum hydroxide mineral, around 6.5 to 7 on the Mohs scale, with perfect cleavage in one direction and a splintery fracture. A useful diagnostic is its tendency to decrepitate, splitting apart with an audible crackle, when heated in a flame. It can be confused with corundum, topaz, or boehmite, though its lower hardness rules out corundum.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Diaspore is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Diaspore worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Diaspore's name comes from the Greek word for scattering, referring to the way it splits apart and crackles audibly when heated.
- Gem-quality diaspore, marketed as zultanite, shifts color from green to pink or champagne depending on the light source, a trait shared with only a few other gemstones like alexandrite.
- Nearly all fine color-change diaspore gems originate from a single mountain range in southwestern Turkey.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
.jpg?width=320)
.jpg?width=320)