Cerchiaraite-(Al)

Chemical formula: Ba₄Al₄(Si₄O₁₂)O₂(OH)₄Cl₂[Si₂O₃(OH)₄]

Cerchiaraite-(Al) is a very rare mineral from the silicate group, prized for its intense blue color and well-formed, prismatic crystals.

## Characteristics Cerchiaraite-(Al) is a complex barium and aluminum silicate belonging to the cerchiaraite group. It forms characteristic, elongated prismatic crystals with a square cross-section, terminated by a pyramid. The most typical specimens are slender, radial aggregates or single, well-formed crystals grown on the host rock. This mineral is valued for its attractive appearance, especially its intense, azure color. ## Physical Properties Crystals are transparent to translucent and exhibit a vitreous luster. The Mohs hardness is approximately 4.5, making it a relatively soft mineral susceptible to scratching. The density is quite high at 3.75 g/cm³. ## Colors and Varieties Cerchiaraite-(Al) occurs in shades from pale blue and sky blue to deep, saturated azure. Colorless crystals are less common. The intensity of the color is the main factor influencing its attractiveness. There are no named commercial or color varieties. ## History and Name The mineral's name comes from its type locality – the Faggiona mine near the town of Cerchiara in Liguria, Italy. It was officially recognized as a new mineral species in 1995. The suffix "-(Al)" in the name indicates that it is a member of the cerchiaraite group in which aluminum (Al) dominates a specific position in the crystal structure. ## Uses Due to its extreme rarity, cerchiaraite-(Al) has no industrial applications. It is exclusively a mineral of scientific and collecting interest, sought after by advanced collectors of rare specimens.

Properties

Mohs hardness: 4.5
Luster: Vitreous
Streak: White
Density: 3.75
Cleavage: Good on {100} and {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Characteristic features of cerchiaraite-(Al) include its tetragonal, prismatic crystals, intense blue color, and specific occurrence environment. Vitreous luster and relatively low hardness are also helpful in identification. ## Distinguishing from Similar Minerals Cerchiaraite-(Al) is sometimes confused with other blue minerals. It differs from benitoite in its crystallographic system (tetragonal vs. trigonal) and paragenesis. It is distinguished from lazurite by its crystalline form (lazurite is a rock-forming mineral and rarely forms distinct crystals). Unlike azurite, cerchiaraite-(Al) does not react with hydrochloric acid. ## Crystal Forms This mineral forms elongated columnar (prismatic) crystals with a square cross-section, often terminated by pyramid faces. Crystals can occur as single individuals or form radial and acicular aggregates.

Geological environment

## Genesis Cerchiaraite-(Al) forms as a result of metamorphic processes within manganese deposits. It forms in veins and lenses cutting through manganese-rich siliciclastic rocks that have undergone alteration under low-grade metamorphic conditions. ## Mineral Associations This mineral coexists with a number of other, often rare, minerals. Its most common associates include sanbornite, bazirite, titantaramellite, walstromite, quartz, barite, and manganese oxides. ## Localities The most important and historical locality is the type locality – the Faggiona mine near Cerchiara in Liguria, Italy. Significant specimens also come from the Wessels mine in the Kalahari manganese field in the Republic of South Africa. It has also been reported in Japan.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized specimens of cerchiaraite-(Al) are characterized by a deep, saturated color, high transparency, and sharply terminated, undamaged crystals. Acicular crystals grown on a contrasting matrix, such as white sanbornite, are particularly sought after. The size of the crystals and the richness of the aggregates also significantly increase their collector's value. ## Popular Localities Two locations are considered the source of the world's best specimens: the Faggiona mine in Italy, from which classic, historical material originates, and the Wessels mine in South Africa, which has provided specimens of exceptionally intense color and excellent crystal form.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. For heavier dirt, distilled water can be used. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to Avoid The mineral is relatively soft (hardness 4.5), so it should be protected from contact with harder minerals (e.g., quartz) that can scratch it. Contact with acids and strong chemicals should be avoided. It does not require special protection from light. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches and mechanical damage. It is best to display them in closed cabinets, protecting them from dust and accidental impact.

Sources

IMA Mineral List (CNMNC)