Rhabdophane-(La)

Chemical formula: LaPO<sub>₄</sub>·H<sub>₂</sub>O

Rhabdophane-(La) is a hydrated lanthanum phosphate, forming small, radial aggregates with a waxy or greasy luster.

## Characteristics Rhabdophane-(La) is a mineral from the rhabdophane group, belonging to the hydrated phosphates. Its name refers to the dominant rare-earth element - lanthanum. It typically occurs as very small, hexagonal crystals that form radial, spherical, or botryoidal aggregates, as well as crusts and coatings. Due to the small size of the crystals, its features are often difficult to observe with the naked eye. ## Physical Properties This mineral is characterized by a waxy, greasy, or vitreous luster. It is translucent to opaque. Its Mohs hardness is 3.5, and its density ranges from 3.94 to 4.01 g/cm³. It is brittle and has an uneven or conchoidal fracture. ## Colors and Varieties Rhabdophane-(La) is most often colorless, white, grayish, yellowish, light brown, or pinkish. There are no distinct commercial or gemological varieties. ## History and Name The name "rhabdophane" comes from the Greek words *rhabdos* (ραβδί) meaning "rod" or "stick" and *phainesthai* (φαίνεσθαι) meaning "to appear," which refers to its characteristic banded absorption spectrum. The suffix "-(La)" was added in 1987 by the International Mineralogical Association (IMA) to indicate lanthanum as the dominant rare-earth element in this particular mineral variety. The original rhabdophane was described by William B. Rogers in 1885. ## Uses Rhabdophane-(La) has no direct industrial applications. However, it is of scientific interest as a rare-earth element-bearing mineral and is valued by collectors specializing in rare minerals or phosphate minerals.

Properties

Mohs hardness: 3.5
Luster: Waxy
Streak: White
Density: 3.94-4.01
Cleavage: Good on {1010}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Field identification is practically impossible without specialized equipment. In a collection, it is recognized by its characteristic forms – radial, spherical aggregates or crusts. A greasy or waxy luster is also a helpful clue. However, definitive confirmation requires advanced analyses, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS) to determine its composition. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphate minerals, such as wavellite or pyromorphite, which also form radial aggregates. Differentiation is based on chemical analysis, as rhabdophane-(La) is the only one among them that contains lanthanum. It can also be confused with other minerals from the rhabdophane group, such as rhabdophane-(Ce) or rhabdophane-(Nd), from which it differs by the dominant rare-earth element. ## Crystal Forms It forms very small, hexagonal, prismatic crystals. Most often, it occurs as radial, fibrous aggregates, as well as spherical clusters (spherulites), botryoidal forms, and earthy or powdery coatings and crusts on other minerals.

Geological environment

## Genesis Rhabdophane-(La) is a secondary mineral. It forms in the oxidation (weathering) zones of ore deposits and pegmatites, as a result of the alteration of primary rare-earth element-bearing minerals such as monazite, bastnäsite, or allanite. It can also crystallize in low-temperature hydrothermal processes and in sedimentary environments, including phosphorites. ## Mineral Associations It often co-occurs with the minerals from which it forms, namely monazite and allanite. It is also accompanied by other secondary phosphates, iron oxides (goethite, hematite), clay minerals (kaolinite), and quartz. ## Localities Significant localities from which well-documented specimens originate include Salisbury, Connecticut (USA), where it was first described. It also occurs in many other places worldwide where rare-earth element-rich rocks weather, e.g., in Russia (Kola Peninsula), Norway, Brazil, and Australia.

Rarity

Rare

For collectors

## Quality Criteria The quality of a rhabdophane-(La) specimen primarily depends on the richness and development of the aggregates. The most prized specimens are those with clearly visible, well-formed spherical or radial clusters on a contrasting matrix. Color intensity, although usually pale, can also affect attractiveness. Due to the microscopic size of the crystals, their individual form is not a key criterion. ## Popular Localities Although it occurs in many places, specimens of collector significance are rare. The locality in Salisbury (Connecticut, USA) is of historical importance. Other localities providing specimens are those known for the occurrence of rare-earth minerals, but specific localities prized by collectors for rhabdophane-(La) are not widely known.

Care and storage

## Cleaning Due to its low hardness and brittleness, it should be cleaned very carefully. The safest method is to use compressed air to remove dust. If wet cleaning is necessary, use a soft brush and distilled water, avoiding strong rubbing. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the mineral's surface. It should not be cleaned in ultrasonic cleaners. It is relatively stable, but sudden temperature changes should be avoided. ## Storage Rhabdophane-(La) specimens are usually small and fragile, so it is best to store them in separate, padded collector boxes to prevent abrasion and mechanical damage. They should be protected from dust and contaminants.

Sources

IMA Mineral List (CNMNC)