DIASPORE

Diaspore: Color Change, Properties, Formation & Care

Diaspore is an aluminum oxyhydroxide mineral known to collectors for its pearly luster and, in some gem-quality material, a noticeable color change under different lighting. Transparent diaspore is marketed as a gemstone under trade names such as zultanite or csarite, but the mineral name remains diaspore.

Quick Facts

  • Mineral class: hydroxide/oxyhydroxide.
  • Chemical formula: AlO(OH).
  • Crystal system: orthorhombic.
  • Mohs hardness: approximately 6.5–7.
  • Some gem material shifts between greenish, yellowish, pinkish, or brownish tones with lighting.

Formation and Geology

Diaspore occurs in aluminum-rich geological settings, including bauxite deposits and metamorphic rocks. It can form during alteration and dehydration reactions involving aluminum-bearing minerals. Its occurrence with corundum and other aluminum-rich minerals reflects the chemistry and history of the host rock.

Geological context helps explain a specimen but does not confirm identification by itself. Diaspore may occur as crystals, aggregates, or grains, and its appearance can vary with impurities and texture.

Color and Optical Effects

Ordinary diaspore can be colorless, white, gray, yellow, brown, or greenish. Some transparent gem material shows a change in apparent color between daylight-like and warmer indoor illumination. The effect depends on the stone’s composition, light source, and observer.

Color change should not be assumed in every diaspore specimen. A gem should be viewed under more than one consistent light source, and trade names should not substitute for accurate mineral identification.

Physical Properties

Diaspore has an orthorhombic crystal structure and Mohs hardness around 6.5 to 7. It has perfect cleavage in one direction, which can make it brittle and challenging to cut. Its luster may appear pearly on cleavage surfaces and vitreous elsewhere.

Cleavage is an important durability consideration for faceted gems. A stone may resist everyday scratching reasonably well yet still chip if struck or set in a vulnerable position.

Gemstone Interest and Localities

Gem-quality diaspore is best known from deposits in Turkey, although diaspore as a mineral occurs in other regions and geological settings. Transparent crystals suitable for faceting are much less common than ordinary mineral occurrences.

Ask for a clear description of the material and any treatments or trade names used. Locality claims should be supported by documentation when origin matters to a collector or buyer.

Identification and Similar Materials

Diaspore can be confused with other pale or color-changing gemstones. A gemologist can examine refractive index, optical behavior, inclusions, and other diagnostic properties. Do not rely on color change alone or on a trade name to establish species identity.

For rough specimens, crystal habit, cleavage, hardness, and geological association are useful clues, but professional analysis may be needed for certainty.

Care and Cleaning

Because of its cleavage,  jewelry should be protected from impacts. Clean gently with lukewarm water, mild soap, and a soft cloth or brush when appropriate. Avoid ultrasonic and steam cleaners, harsh chemicals, and sudden temperature changes.

Store separately from harder gemstones and consider protective settings for rings or pieces worn frequently. Keep mineral specimens in padded display spaces so projecting edges are not knocked.

Frequently Asked Questions

Does all diaspore change color?

No. Color change is a feature of some gem-quality material, not every specimen.

Is zultanite a separate mineral?

No. Zultanite is a trade name used for certain gem-quality diaspore material.

Further Reading & Sources

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