Fogoite-(Y)

Chemical formula: Ca₂Y₂Na₃Ti⁴⁺(Si₂O₇)₂(OF)F₂

Fogoite-(Y) is a very rare mineral from the rosenbuschite group, discovered on the volcanic island of Fogo, distinguished by its complex chemical composition with the presence of yttrium and titanium.

## Characteristics Fogoite-(Y) is a silicate with a very complex chemical structure, belonging to the rosenbuschite group within the seidozerite supergroup. This mineral forms very small, lath-like or acicular crystals, reaching up to 150 micrometers in length and up to 20 micrometers in width. It usually occurs as radial or randomly oriented aggregates embedded in other minerals. It is colorless and transparent, with a vitreous luster. ## Physical properties Due to the microscopic size of its crystals, many physical properties have not been fully investigated. Hardness is estimated to be approximately 5 on the Mohs scale. The density calculated from the formula and unit cell parameters is 3.45 g/cm³. The mineral does not exhibit fluorescence under ultraviolet light. ## Colors and varieties Fogoite-(Y) is colorless. No colored varieties are known. ## History and name The mineral's name refers to its discovery locality – the volcanic island of Fogo in the Cape Verde archipelago. The suffix -(Y) indicates the dominant rare-earth element in its composition, which is yttrium. Fogoite-(Y) was approved as a new mineral species by the International Mineralogical Association (IMA) in 2014 (IMA number 2014-038). It was described by an international team of researchers, including Joel Grice and G. Chukanov. ## Uses Fogoite-(Y) has no industrial or commercial applications. Its significance is purely scientific and as a collector's item, as a unique and rare representative of silicates.

Properties

Mohs hardness
5
Color
Colourless; creamy white
Luster
Vitreous
Streak
White
Density
3.523
Cleavage
{100}
Fracture
Splintery
Transparency
Transparent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of fogoite-(Y) is impossible without advanced laboratory techniques. Due to the microscopic size of the crystals, chemical analysis (e.g., using an electron microprobe - EDS/WDS) is required to confirm its unique composition with the presence of Ca, Y, Na, Ti, and Si. Structural analysis, e.g., by X-ray diffraction (XRD), is also necessary. ## Distinguishing from similar minerals Fogoite-(Y) is visually indistinguishable from other microscopic, colorless minerals of the rosenbuschite group, such as rosenbuschite, götzenite, or hainite. The differences between them lie in subtle changes in chemical composition (e.g., dominance of zirconium, niobium, or various rare-earth elements) and structural parameters, which require specialized research equipment. ## Crystal forms The mineral forms elongated, lath-like or acicular crystals, often flattened. They occur as single needles embedded in other minerals or form small, radial aggregates.

Geological environment

## Genesis Fogoite-(Y) forms in the late stages of crystallization in a specific geological environment. It was found in syenitic xenoliths (fragments of intrusive rocks) entrained and brought to the surface by phonolitic lava during a volcanic eruption. ## Mineral associations This mineral co-occurs with other rare minerals within the xenoliths. Its typical associations include: aegirine, nepheline, fluorite, eudialyte, astrophyllite, as well as other minerals from the rosenbuschite group. ## Localities The only confirmed occurrence of fogoite-(Y) in the world is its type locality: syenitic xenoliths found within the Pico do Fogo volcanic cone on Fogo Island, Republic of Cape Verde.

Rarity

Extremely rare

For collectors

## Quality criteria As a microscopic mineral, fogoite-(Y) is primarily valued for its confirmed presence on a specimen. Samples in which fogoite-(Y) aggregates are relatively "rich" and clearly visible under a microscope are most highly rated. Association with other rare minerals is also important, as it increases the scientific and collector's value of the specimen. Identification must be analytically confirmed. ## Popular localities The only source of specimens is the type locality on Fogo Island. Material from this location is extremely rare on the collector's market and is almost exclusively available through research institutions or specialized micromount collectors.

Care and storage

## Cleaning Specimens containing fogoite-(Y) should be handled with extreme caution due to the microscopic size and fragility of the crystals. Cleaning is not recommended, but if absolutely necessary, compressed air can be used from a safe distance to remove dust. Any contact with water, chemicals, or brushes should be avoided. ## What to avoid Ultrasonic cleaners, acids, solvents, and all chemical agents must be strictly avoided. The mineral is sensitive to shocks and impacts, which can destroy delicate crystals. Abrupt temperature changes should also be avoided. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" boxes that protect them from dust, moisture, and mechanical damage. Exposure to strong light is not recommended, although there is no confirmed data on its effect.

External references

Sources

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