Lucasite-(La)

Chemical formula: LaTi₄+₂O₅(OH)

Lukassite-(La) is an extremely rare, reddish-brown lanthanum titanate mineral, found as microscopic crystals in Australia.

## Characteristics Lukassite-(La) is a lanthanum and cerium titanate, belonging to the crichtonite group. It forms very small, tabular or prismatic crystals, reaching sizes up to approximately 200 micrometers. It typically occurs as single, scattered crystals within the host rock. It is a translucent mineral with a reddish-brown color and a resinous luster. ## Physical Properties Due to the microscopic size of the crystals, many physical properties have not been fully investigated. Hardness is estimated at approximately 6 on the Mohs scale. The density calculated from the formula and unit cell parameters is 5.01 g/cm³. The mineral exhibits strong pleochroism in shades from reddish-brown to yellowish-brown. ## Colors and Varieties This mineral occurs in a uniform, reddish-brown color. No color varieties or commercial forms are known. ## History and Name Lukassite-(La) was discovered in samples from the Walgidee Hills in the Kimberley district of Western Australia. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1987. Its name honors the Australian analytical chemist, Dr. Howard Keith Lucas, for his contributions to rare-earth mineral chemistry. The suffix "-(La)" indicates lanthanum as the dominant rare-earth element in its chemical composition.

Properties

Mohs hardness: 6
Luster: Resinous
Streak: Red-brown
Density: 5.01
Cleavage: None
Fracture: Conchoidal
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of lukassite-(La) is impossible without advanced laboratory techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the composition with dominant lanthanum and titanium, and X-ray diffraction (XRD) to determine the crystal structure. Visually, at the occurrence site, it can be suspected based on its reddish-brown color, resinous luster, and co-occurrence with other minerals from the crichtonite group. ## Distinguishing from Similar Minerals It can be confused with other minerals from the crichtonite group, such as senaite, davidite, or crichtonite, which have a similar appearance and occur in the same environment. Definitive distinction is possible only through detailed chemical analysis, which will show the dominance of lanthanum over other rare-earth elements. ## Crystal Forms The crystals are very small, with a tabular or short-prismatic habit, often with a hexagonal outline. They occur as single, isolated crystals within the host rock.

Geological environment

## Genesis Lukassite-(La) forms during metasomatic processes within lamproites – rare, ultrapotassic igneous rocks rich in potassium. It is an accessory mineral, crystallizing in the late stages of these rocks' formation, in the presence of rare-earth elements and titanium. ## Mineral Associations This mineral co-occurs with other rare minerals typical of lamproites, such as priderite, wadeite, jeppeite, richterite, ilmenite, perovskite, shcherbakovite, and apatite. ## Localities The only confirmed occurrence (type locality) of lukassite-(La) in the world is in the lamproites of Walgidee Hills in the Kimberley region of Western Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, lukassite-(La) is primarily valued by collectors specializing in "micromounts" and rare and systematic minerals. Specimens showing well-formed, sharp crystals, clearly contrasting with the rock matrix, are most highly prized. The size (even if measured in micrometers) and abundance of crystals on the specimen also increase its value. ## Popular Localities The only source of specimens is the type locality in Walgidee Hills, Australia. Material from this location is extremely difficult to acquire.

Care and storage

## Cleaning Specimens of lukassite-(La) should be handled with extreme care due to the microscopic size and rarity of the crystals. Cleaning is usually not necessary or recommended. If absolutely required, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Ultrasonic cleaners, chemical agents, acids, and sudden temperature changes must be strictly avoided. The crystals are fragile and embedded in a matrix, so the specimen should be protected from impacts and vibrations. ## Storage Specimens should be stored under stable conditions, in a sealed "micromount" box, to protect them from dust and mechanical damage. Storage in darkness is not necessary, but prolonged exposure to intense light is recommended to be avoided.

Sources

IMA Mineral List (CNMNC)