Lucasite-(Ce)

Chemical formula: Ce³⁺Ti⁴⁺₂O₅(OH)

Lucasite-(Ce) is a rare cerium and titanium oxide, forming small, prismatic crystals of a reddish-brown color.

## Characteristics Lucasite-(Ce) is a very rare mineral from the oxide group, chemically classified as a cerium and titanium oxyhydroxide. It occurs as very small, elongated, prismatic crystals, rarely exceeding 1 mm in length. Crystals are often grouped into radial or randomly oriented aggregates. Its characteristic feature is an intense, reddish-brown to orange-brown color. ## Physical Properties This mineral is characterized by an adamantine luster, which gives it a vivid appearance despite its small size. It is transparent to translucent. Due to the size of the crystals, hardness has not been precisely measured, but it is estimated to be around 6.5 on the Mohs scale. The density calculated based on the formula and cell parameters is 5.01 g/cm³. ## Colors and Varieties Lucasite-(Ce) occurs in uniform colors ranging from reddish-brown to orange-brown. No varieties have been distinguished. ## History and Name The mineral was named after the Australian chemist and mineralogist A. H. S. Lucas (1853-1936), who made significant contributions to the study of minerals in Western Australia. The "-(Ce)" suffix in the name indicates the dominant rare-earth element – cerium. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1986, and its description was published in 1987. The discovery was made based on samples from the Argyle diamond mine in Western Australia.

Properties

Mohs hardness
6
Color
Brown, grey
Luster
Resinous
Streak
Pale brown
Density
0
Cleavage
Good on {001}, may be a parting
Fracture
Sub-Conchoidal
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying lucasite-(Ce) under amateur conditions is practically impossible. Identification requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD), to confirm its chemical composition and crystal structure. Visually, it can be suspected based on its reddish-brown color, adamantine luster, prismatic crystal form, and co-occurrence with other minerals from lamproites. ## Distinguishing from Similar Minerals It can be confused with other small, reddish titanium minerals, such as rutile or brookite, which may occur in similar environments. Definitive differentiation is only possible through chemical analysis, which will show the presence of cerium as a key component. ## Crystal Forms It forms elongated, prismatic crystals with a nearly square cross-section. Crystals often occur as radial aggregates or irregular clusters within the host rock (lamproite).

Geological environment

## Genesis Lucasite-(Ce) is a mineral of magmatic origin. It forms as an accessory mineral in potassium-rich volcanic rocks called lamproites. It crystallizes in the late stages from residual, rare-earth and titanium-enriched lamproitic magma. ## Mineral Associations This mineral co-occurs with other minerals typical of lamproites, such as priderite, wadeite, jeppeite, richterite, diopside, perovskite, apatite, and phlogopite. ## Localities The only confirmed and described occurrence (type locality) of lucasite-(Ce) is the Argyle lamproite pipe in the Kimberley region of Western Australia. This is also the world's largest diamond mine.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of lucasite-(Ce) specimens is primarily assessed based on the size and development of the crystals and their abundance on the rock matrix. The most prized specimens are those with clearly visible, sharp, prismatic crystals of intense, reddish-brown color, forming visually attractive aggregates. Contrast with the lighter host rock also enhances aesthetic value. ## Popular Localities The only source of collector specimens is the Argyle diamond mine in Western Australia. Due to the mine's closure in 2020, the availability of material on the market is extremely limited, and no new specimens will be acquired.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to extreme rarity and small crystal sizes, any mechanical or chemical contact should be avoided. ## What to Avoid Contact with water, chemicals, acids, and ultrasonic cleaners must be absolutely avoided. The crystals are brittle and embedded in a matrix, so any shock or attempt at mechanical cleaning can permanently damage them. ## Storage Lucasite-(Ce) specimens should be stored in stable conditions, in closed "micromount" boxes, to protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and temperature changes.

External references

Sources

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