Lucchesiite

Chemical formula: CaFe²⁺₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃O

Lucchesiite is a very rare, black mineral from the tourmaline group, distinguished by its complex chemical composition with a dominance of calcium and iron.

## Characteristics Lucchesiite is a mineral belonging to the tourmaline group. Its crystals are typically black and opaque. As a member of the tourmaline supergroup, it shares the characteristic elongated, prismatic habit with typical striations along the main crystal axis. It is a relatively recently described mineral, and its specimens are extremely rare, making it primarily an object of scientific interest and specialized collections. ## Physical Properties This mineral is characterized by a hardness of 7 on the Mohs scale, which is typical for tourmalines. Its density, calculated from crystallographic data, is 3.226 g/cm³. It has a vitreous to resinous luster and a conchoidal fracture. It is brittle. ## Colors and Varieties Lucchesiite occurs in a uniform, black color. Due to its recent discovery and rarity, no color varieties or trade names have been identified. ## History and Name The mineral was named in honor of Massimo Lucchesi (born 1952), a professor of mineralogy at Sapienza University in Rome, Italy. His research significantly contributed to the understanding of the crystal chemistry of tourmaline group minerals. The mineral was officially recognized by the International Mineralogical Association (IMA) in 2015. ## Uses Due to its extreme rarity, lucchesiite has no industrial or commercial applications. Its significance is purely scientific and for collectors.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: Grey
Density: 3.226
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identifying lucchesiite in the field is practically impossible without advanced analytical methods. In a collection, it can be preliminarily identified based on its black color, prismatic crystal habit with characteristic striations along the crystallographic axis, and hardness (7 on the Mohs scale). However, definitive identification requires chemical analysis (e.g., using an electron microprobe) to determine its unique composition, particularly the dominance of calcium at the X site and iron at the Y site in the tourmaline structure. ## Distinguishing from Similar Minerals Lucchesiite is visually indistinguishable from other black tourmalines, such as schorl, dravite, or foitite. Schorl is the most common black tourmaline and has sodium at the X site. Dravite is enriched in magnesium, and foitite is characterized by a vacancy at the X site. Final differentiation of these minerals is possible only through detailed chemical analysis. ## Crystal Forms Lucchesiite forms prismatic crystals, often terminated by complex trigonal pyramidal faces. The prism faces exhibit longitudinal striations characteristic of tourmalines. The cross-section of the crystal is typically a rounded triangle.

Geological environment

## Genesis Lucchesiite, like other tourmalines, crystallizes in boron-rich environments. Its formation is associated with metamorphic and hydrothermal processes. In its type locality in the Czech Republic (Mirošov), it occurs within marbles (carbonate rocks transformed under high temperature and pressure conditions), which explains the presence of calcium in its composition. In Sri Lanka, it has been found as pebbles in alluvial sediments, indicating its origin from weathered primary rocks. ## Mineral Associations Minerals co-occurring with lucchesiite in the Czech locality include calcite, diopside, phlogopite, titanite, and other tourmalines (dravite, uvite). In Sri Lanka, as a heavy mineral, it occurs in alluvial concentrates along with corundum, spinel, zircon, and other tourmalines. ## Localities Confirmed occurrences of lucchesiite, which are also its type localities, are Mirošov near Žďár nad Sázavou in the Czech Republic and alluvial deposits in the Ratnapura area of Sri Lanka. These are the only known places from which specimens of this mineral originate.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of lucchesiite specimens is primarily assessed based on crystal development and size. Well-formed, single crystals with distinct faces and terminations, and visible striations, are most desirable. Specimens on matrix, especially in association with other minerals from the type locality, are particularly valued. Luster and the depth of the black color also contribute to the aesthetic appeal of the specimen. ## Popular Localities Both type localities – Mirošov in the Czech Republic and Ratnapura in Sri Lanka – provide specimens valued by collectors. Czech specimens, often found in marble, are of great scientific importance due to their known geological context. Specimens from Sri Lanka, being pebbles, may be larger, but their primary source is unknown.

Care and storage

## Cleaning Given its hardness of 7 on the Mohs scale, lucchesiite is relatively scratch-resistant. For cleaning, it is recommended to use a soft brush and distilled water. Ultrasonic cleaners can also be used, but with caution, especially for specimens with inclusions or fractures. ## What to Avoid Contact with strong acids should be avoided, especially hydrofluoric acid, which can damage the crystal surface. Although it is a stable mineral, rapid temperature changes are not recommended, as they could induce internal stresses and cracks. ## Storage Lucchesiite specimens are best stored in separate, padded boxes to prevent abrasion and mechanical damage from contact with other minerals. As a stable mineral, it does not require special conditions regarding humidity or light exposure.