Deltalumite
Chemical formula: (Al₀.₆₇◻₀.₃₃)Al₂O₄
Deltalumite is a very rare aluminum oxide from the spinel group, forming microscopic, tetragonal crystals in volcanic eruption products.
Properties
- Luster
- Vitreous
- Density
- 3.663
- Transparency
- Translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification Identification of deltalumite is only possible using advanced laboratory techniques, such as X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). Under collector or field conditions, identification is impossible due to the microscopic size of the crystals. ## Distinguishing from Similar Minerals Based on visual characteristics alone, it is impossible to distinguish from other microscopic, light-colored oxide minerals coexisting in the same environment, such as corundum, hematite, or other spinels. Reliable differentiation requires analysis of the crystal structure and chemical composition. ## Crystal Forms It forms very small, tabular or pyramidal (dipyramidal) crystals with a square cross-section, reaching up to 15 μm in size. They occur as single crystals or in loose aggregates.
Geological environment
## Genesis Deltalumite forms in a unique environment of high-temperature (above 600 °C) volcanic exhalations (fumaroles). It crystallizes directly from volcanic gases under oxidizing conditions, depositing on basaltic volcanic ash. ## Mineral Associations At its discovery site, it coexists with other minerals formed in a similar way, such as hematite, corundum, ktenasite, chalcanthite, atlasovite, florenskyite, antlerite, and brochantite. ## Localities The only confirmed locality of deltalumite in the world is its type locality – the fumarole products formed after the eruption of Plosky Tolbachik volcano in 2012-2013 on the Kamchatka Peninsula, Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria As a mineral of purely scientific significance and for specialized micromineral collectors, the value of a specimen depends on the confirmed presence of deltalumite. Samples where the crystals, despite their microscopic size, are relatively well-formed and abundant are most highly valued. Precise documentation and a label with analytical confirmation are crucial. ## Popular Localities The only source of specimens is the type locality at Plosky Tolbachik volcano in Kamchatka.
Care and storage
## Cleaning Due to the extremely small size of the crystals and their occurrence as inclusions in the rock, specimens containing deltalumite do not require and should not undergo mechanical or chemical cleaning. Any attempt at cleaning risks irreversible destruction of the microscopic crystals. ## What to Avoid Contact with any chemicals, ultrasound, and all forms of physical intervention (e.g., brushing, scraping) should be avoided. Specimens should be protected from dust and contaminants. ## Storage Deltalumite specimens, as microminerals, should be stored in specialized, sealed "micromount" boxes that protect them from dust, moisture, and mechanical damage. They do not require special lighting conditions.