Cassagnaite

Chemical formula: Ca₄Fe₃+₄V₃+₂(OH)₆O₂(Si₃O₁₀)(SiO₄)₂

Cassagnaite is a very rare silicate mineral, discovered in Italy, forming tiny, hexagonal crystals of a brownish-red color.

## Characteristics Cassagnaite is a complex calcium, iron, and vanadium silicate, belonging to the ardennite group. It occurs as very small, hexagonal, tabular crystals, not exceeding 0.2 mm. These crystals form rosetted or randomly oriented aggregates. It is a mineral with a brownish-red color and a vitreous luster. ## Physical Properties Due to the extremely small size of the crystals, most physical properties, such as hardness, density, cleavage, or fracture, have not been precisely determined. The mineral is brittle. ## Colors and Varieties Only a brownish-red color has been observed. The mineral is translucent. No varieties have been distinguished. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2013 under number 2013-031. Its name honors Giovanni Cassagna (born 1952), an Italian mineral collector from Varese, who found the first samples of this mineral. The scientific description was published in 2016 by a research team led by Ferdinando Bosi. ## Applications Cassagnaite has no industrial applications. Its significance is purely scientific and as a collector's item, as a unique representative of vanadium silicates.

Properties

Mohs hardness: 5.5
Luster: Vitreous
Streak: Light brown
Density: 3.65
Cleavage: None
Fracture: Uneven
Transparency: Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of cassagnaite is only possible using advanced analytical methods, such as Raman spectroscopy, electron microprobe analysis (EMPA), and single-crystal X-ray diffraction. For collectors, identification relies on a label from a confirmed locality and the characteristic morphology of microscopic, hexagonal crystals in association with other minerals from that locality. ## Distinguishing from Similar Minerals It can be confused with other rare minerals from the ardennite group, such as ardennite-(As) or ardennite-(V), which have a similar appearance and occur in similar environments. Definitive differentiation requires specialized laboratory investigations. ## Crystal Forms It forms very small, tabular, hexagonal (six-sided) crystals, which often combine into rosetted aggregates.

Geological environment

## Genesis Cassagnaite forms as a result of metamorphic processes in manganese deposits. In its type locality (Valgraveglia mine), it occurs in hematite-braunite veins cutting manganese-rich jaspers. ## Mineral Associations This mineral coexists with hematite, braunite, quartz, ardennite-(V), ganophyllite, piemontite, cryptomelane, and palenzonaite. ## Localities The only confirmed occurrence worldwide is its type locality: the Valgraveglia mine, located near the town of Ne in the Graveglia Valley, Liguria, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the quality of a specimen is primarily determined by the abundance and development of crystals on the rock matrix. Specimens with numerous, well-formed, rosetted cassagnaite aggregates, clearly visible under a microscope, are most valued. Contrast with surrounding minerals, such as quartz, also enhances aesthetic value. ## Popular Localities All specimens available on the collector's market come from a single location worldwide – the Valgraveglia mine in Italy. This is the type locality and the only known one.

Care and storage

## Cleaning Specimens should be handled with the utmost care. Due to the microscopic size and brittleness of the crystals, mechanical or chemical cleaning is not recommended. It is safest to leave the specimen in its untouched state. ## What to Avoid Avoid contact with any chemicals, ultrasonic cleaners, and sudden temperature changes. The crystals are very brittle and easily susceptible to mechanical damage. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" boxes, to protect them from dust and physical damage. Vibrations and shocks should be avoided.

Sources

IMA Mineral List (CNMNC)