Deloneite
Chemical formula: (Na₀.₅REE₀.₂₅Ca₀.₂₅)(Ca₀.₇₅REE₀.₂₅)Sr₁.₅(CaNa₀.₂₅REE₀.₂₅)(PO₄)₃F₀.₅(OH)₀.₅
Deloneite is a rare, bright yellow mineral from the belovite group, being a complex phosphate of strontium, calcium, sodium, and rare earth elements.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.92
- Cleavage
- <mi>{1010}</mi> and <mi>{0001}</mi>
- Fracture
- Step-Like
- Transparency
- Transparent
- Crystal system
- Trigonal
Diagnostic features
## Identification Deloneite can be identified by its characteristic bright yellow color, hexagonal crystal habit, and occurrence in a specific geological environment – alkaline pegmatites. Vitreous luster and a Mohs hardness of 5 are also important auxiliary features. ## Distinguishing from Similar Minerals It can be confused with other yellow phosphates from the apatite or belovite group. It differs from apatite by its higher density and specific paragenesis. Accurate identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical composition analysis (EDS/WDS). ## Crystal Forms It forms elongated, prismatic crystals with a hexagonal cross-section. They often occur as radial or acicular aggregates intergrown with other minerals.
Geological environment
## Genesis Deloneite is a hydrothermal mineral, crystallizing in the late stages of the evolution of ultra-alkaline pegmatites. It forms in veins cutting through nepheline syenite massifs. ## Mineral Associations This mineral co-occurs with other rare alkaline minerals. In the type locality, it was found in association with aegirine, natrolite, microcline, lorenzenite, lomonosovite, eudialyte, and other phosphates from the belovite group. ## Localities The only confirmed and thoroughly described occurrence of deloneite in the world is its type locality – the Koashva mine outcrop on the mountain of the same name, in the Khibiny Alkaline Massif on the Kola Peninsula in Russia.
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and transparent crystals of intense yellow color. Rich crystal aggregates or single crystals contrasting with a darker matrix, e.g., with aegirine, are particularly sought after. Crystal size is a key factor, as most of them are very small. ## Popular Localities The only source of collectible specimens is the Khibiny Alkaline Massif on the Kola Peninsula in Russia. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Deloneite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, followed by thorough drying of the specimen. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is sensitive to strong acids, which can damage it. Avoid sudden temperature changes and prolonged exposure to direct sunlight, which could theoretically affect its color. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to protect them from scratching by harder minerals. They should be protected from dust and moisture.