Fluoro-cannilloite

Chemical formula: CaCa₂(Mg₄Al)(Si₅Al₃)O₂₂F₂

Fluoro-cannilloite is a very rare mineral from the amphibole group, a member of the cannilloite series, distinguished by the dominance of fluorine.

## Characteristics Fluoro-cannilloite is a mineral from the silicate group, belonging to the calcic amphiboles. It forms elongated, prismatic crystals, usually small, reaching up to 1 mm in length. Most often, it occurs as inclusions in other minerals or as a component of aggregates. It is a transparent to translucent mineral with a vitreous luster. ## Physical Properties The mineral is characterized by a hardness in the range of 5-6 on the Mohs scale. Its density is slightly higher than quartz, approximately 3.16 g/cm³. The crystals exhibit perfect cleavage in two directions, which is typical for amphiboles. ## Colors and Varieties Fluoro-cannilloite is colorless. Due to its extreme rarity and occurrence as microscopic crystals, no colored or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of fluorine (Fluoro-) and its association with other minerals from the cannilloite series (-cannilloite), named after the Italian mineralogist Francesco Cannillo (1936–1993). It was formally described and approved as a new mineral by the International Mineralogical Association (IMA) in 2003 (IMA2003-035).

Properties

Mohs hardness
6
Color
Grey-green
Luster
Vitreous
Streak
Grey-white
Density
3.05
Cleavage
On {110}, intersecting at ~56°.
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of fluoro-cannilloite is impossible without advanced analytical techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm its composition, especially the dominance of fluorine and the magnesium to aluminum ratio. Optically, it is indistinguishable from other colorless amphiboles. ## Distinguishing from Similar Minerals It can be confused with other minerals from the amphibole group, such as tremolite, edenite, pargasite, or other minerals from the cannilloite series. Differentiation relies solely on precise chemical composition analysis. ## Crystal Forms It forms columnar or prismatic crystals, often acicular. It occurs as single, dispersed crystals within the matrix rock or in small aggregates.

Geological environment

## Genesis Fluoro-cannilloite forms under conditions of high-grade contact metamorphism, in contact zones of magmatic intrusions with carbonate rocks (e.g., marbles). It is a product of reactions occurring at high temperatures and pressures. ## Mineral Associations This mineral co-occurs with other minerals typical of skarns and marbles, such as calcite, dolomite, forsterite, spinel, phlogopite, pargasite, and other amphiboles. ## Localities The only confirmed occurrence (type locality) is the Crestmore quarry in Riverside County, California, USA. This is a classic locality for many rare contact-metamorphic minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, fluoro-cannilloite is primarily valued by collectors specializing in rare and systematic minerals (so-called "micromounters"). The value of a specimen is determined primarily by the certainty of identification (analytical confirmation), the abundance of its occurrence on a fragment of the matrix rock, and the presence of well-formed, even if microscopic, crystals. Association with other rare minerals also increases its value. ## Popular Localities The only source of specimens is the historical type locality – the Crestmore quarry in California. Material from this location is highly sought after due to its scientific significance.

Care and storage

## Cleaning Specimens containing fluoro-cannilloite, due to their microscopic nature and occurrence within the matrix rock, generally do not require cleaning. If necessary, use only compressed air to remove dust. ## What to Avoid Avoid contact with all chemicals, including acids and strong bases. Do not use ultrasonic cleaners, which could damage delicate crystals or the matrix rock. The mineral is stable under normal conditions, but extreme temperatures should be avoided. ## Storage Specimens should be stored in stable conditions, away from dust and moisture, preferably in a sealed display box or cabinet. Due to the small size of the crystals, storage in "micromount" boxes with appropriate labeling is recommended.

External references

Sources

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