97Materials libraryDiaspore: bounded material evidenceAn aluminium oxyhydroxide with orthorhombic structure and brittle behavior.
Evidence remains bounded by each cited work; no unrecorded specimen is identified.
- Formula
- AlO(OH)
An oxyhydroxide species
The Handbook of Mineralogy gives Diaspore the formula AlO(OH). It has orthorhombic symmetry, a type of crystal structure. The species is an aluminium oxyhydroxide. Boehmite is its dimorph. They share chemistry but not structure, so the names do not mean the same thing. The reference lists flat, platy crystals. Others are long or needle-like, or form less ordered groups. Perfect {010} cleavage makes a set plane along which it can split. The mineral is very brittle. Hardness alone cannot tell us how it will break. The account lists bauxite diagenesis, changes within that rock. It also lists hydrothermal alteration of aluminous minerals, where hot water alters minerals rich in aluminium. Some alkaline pegmatites are listed too. The Greek-derived name refers to scattering when heated with a blowpipe. That explains a historical name. It gives no reason to damage a piece with this test.
Evidence: Handbook of Mineralogy: Diaspore
A colour comparison with corundum
Shen and Lu studied gem Diaspore and corundum in Winter 2018. They used spectroscopy and trace-element tests. The two structures share some features. How do known colour-producing ions act in a different host? The team linked colour change to chromium, vanadium and iron–titanium pairs. Absorption was around 560–580 nanometres. They compared measured amounts, with limits. Some pictured colours were calculated for set amounts and light path lengths. They were not photos of a stone in those exact conditions. Raman tests first helped find the crystal’s direction. The team then compared absorption spectra along different paths. The same chromophores, the sources of colour, had different effects in the two minerals. Vanadium had more effect in their Diaspore calculations. Several other contributors had more effect in corundum. The study asks one question in two distinct structures. It does not turn this mineral into sapphire. A light response alone cannot name a gem. The amounts, crystal direction and light path still matter.
Evidence: The Color Origin of Gem Diaspore: Correlation to Corundum
Purplish pink: reported provenance
Nicastro and colleagues studied purplish pink Diaspore in Summer 2020. They got it from gem dealers. The reported source was Afghanistan; that origin was not verified. The authors called the stones market-collected F-type samples. They had not taken them from the deposit. A microscope showed long fluid inclusions. Some held gas, liquid and, at times, solid phases. Raman tests found rutile needles in two rough samples. A brown hexagonal inclusion was not identified. They saw three pleochroic colours, linked to viewing direction. Under incandescent light, cut stones shifted slightly from purplish pink towards pink. The main hue did not distinctly change. A cube cut to known directions let them study spectra along different paths. Dealers said an earlier gamma-irradiation trial had made unwanted brownish orange colours. The authors did not pursue the test. The trial is a dealer report. The optics and inclusions are findings on these samples. They prove neither a general treatment practice nor a place of origin.
Evidence: Purplish Pink Diaspore Reportedly from Afghanistan
A Tokyo laboratory cat’s-eye case
Okada’s Fall 2020 laboratory note concerns one cabochon. It weighed 60.71 carats and was tested in Tokyo. Refractive-index readings, a biaxial optic result and a Raman match supported the name Diaspore. Its colour changed with the light. It looked greenish yellow in daylight-equivalent or fluorescent light. Incandescent light made it pinkish brown. Its narrow eye needed its own explanation. A microscope showed reflecting films and fissures along repeated cleavage planes. The cause was not limited to needles or tubes. These features gave the reported chatoyant look, an eye-like band. Some fissures reached the surface. The team detected no clarity enhancement in this stone. That finding cannot cover all such stones or every cat’s-eye specimen. The case joins three findings: identity, colour under stated light, and a particular reflecting structure. Colour change and chatoyancy still need separate observations. They can occur together without being the same effect.
Evidence: Color-Change Cat’s-Eye Diaspore
A secondary crystal-growth model in Turkey
Hatipoğlu’s 2010 account concerns the İlbir Mountain area of southwestern Turkey. It links gem-quality Diaspore to metabauxite and marble. Its proposed history starts with bauxitic material in karst depressions, hollows in the rock. Regional metamorphism later changed this material. Tectonic fractures and cavities opened spaces. Some constituents moved again and could grow as crystals there. This was secondary mineralisation, a later stage of mineral growth. The larger crystals belong to that stage. They are not simply the first product of weathering. Muscovite, chloritoid and other minerals help describe the group in this study. The account sets apart an aluminium-rich rock body and clear crystals in its openings. This is a dated view of links at one place. It cannot explain all Diaspore. The paper’s broader historical claims that it occurs nowhere else are not used here. The retained sequence joins weathering, metamorphism, fractures and later crystallisation in this setting.
Evidence: Gem-Quality Diaspore Crystals as an Important Element of the Geoheritage of Turkey
Prisms, pinacoids and V-shaped twins
Hatipoğlu and Chamberlain described crystals from Pınarcık in 2011. They listed single crystals, groups, contact twins and groups of twins. Some were blocky; others were flat prisms. The blocky forms had chiefly {100} and {010} pinacoids, pairs of parallel faces. Flat forms had strongly grooved {110} prism faces. Their cross-section was diamond-shaped. Ends with {061} could be balanced or distorted. One face could dominate a distorted end. The authors described V-shaped contact twins. Their composition plane, where the twins join, was (061). Some crystals had bent through later deformation. These facts link visible shapes to structure. They do not make all V-shaped outlines the same. Colours varied in daylight and incandescent light. Both light and crystal direction were part of those views. They do not give the species one fixed colour. The account concerns this occurrence and its recorded forms. Its photos and idealised drawings are not reused here.
Evidence: A Gem Diaspore Occurrence near Pinarcik, Mugla, Turkey
Interpreting hydroxyl motion
Delattre and colleagues’ study came out online in 2011 and in the 2012 journal volume. It joined single-crystal Raman tests, infrared spectra and theoretical calculations. For Raman, they used a natural, colourless gem-quality crystal. Its faces were cut along crystal planes. For infrared work, they used powder mixed in a potassium bromide pellet. They measured it from 50 to 270 kelvin. These were different ways to prepare and view the material. The team asked how particle shape affects powder spectra. Their calculations linked major bands to motion in the structure. The broad hydroxyl-stretching response was more complex. It involved links between modes and hydrogen bonding. Changes with temperature helped explain extra bands as bending overtones. They were not assigned to separate minerals. The study links formula to motion in a crystal. It is not a cleaning test or a growth demonstration. It cannot give an unknown gem this crystal’s history. Its result describes measured vibrational behaviour under stated conditions.
Evidence: Experimental and theoretical study of the vibrational properties of diaspore (α-AlOOH)
Neutrons add a different view of the structure
Wang and colleagues’ paper came out online in 2025 and in a 2026 volume. It compared aluminium hydroxides and oxyhydroxides. They used inelastic neutron scattering and calculations. Their Diaspore was a natural, gem-quality sample from Pınarcık. They ground it for the test. Other comparison phases were made separately. That distinction matters. Making boehmite or gibbsite does not show that they grew Diaspore. The VISION instrument at Oak Ridge measured powders cooled to 15 kelvin. The account describes edge-linked aluminium octahedral strips. It also describes hydrogen bonds in tunnel spaces. It calls this structure non-layered, though it has perfect cleavage. The team compared strong bending bands with infrared and Raman tests. They separated a low-energy instrumental artefact from mineral features. This adds a different test method to the structural account. Its measurement limits still matter. The experiment did not test how well a cut gem withstands wear.
Sources & reading
- Handbook of Mineralogy: DiasporeMineral Data Publishing · 2026-10-06
Study-bound.
- The Color Origin of Gem Diaspore: Correlation to CorundumGIA · 2026-10-06
Study-bound.
- Purplish Pink Diaspore Reportedly from AfghanistanGIA · 2026-10-06
Study-bound.
- Color-Change Cat’s-Eye DiasporeGIA · 2026-10-06
Study-bound.
- Gem-Quality Diaspore Crystals as an Important Element of the Geoheritage of TurkeyGeoheritage · 2026-10-06
Study-bound.
- A Gem Diaspore Occurrence near Pinarcik, Mugla, TurkeyRocks & Minerals · 2026-10-06
Study-bound.
- Experimental and theoretical study of the vibrational properties of diaspore (α-AlOOH)Physics and Chemistry of Minerals · 2026-10-06
Study-bound.
- Libration of hydroxyl groups in layered aluminum (oxy)hydroxides and other material analogs: insights from inelastic neutron scattering and theoryPhysical Chemistry Chemical Physics · 2026-10-06
Study-bound.
