Davidite-(La)

Chemical formula: La₃+(Y,U₄+)Fe₃+₂(Ti₄+,Fe₃+,Cr₃+,V₅+)₁₈(O,OH,F)₃₈

Davidite-(La) is a rare, black oxide mineral of the crichtonite group, containing lanthanum, uranium, and titanium, known for occurring in a metamict state.

## Characteristics Davidite-(La) is a complex oxide belonging to the crichtonite group. It occurs as anhedral, granular masses or, less commonly, as poorly formed, tabular or thick-tabular crystals with a trigonal outline. Its surface is usually dull or covered with weathering products. This mineral is most often metamict, meaning its internal crystal structure has been destroyed by ionizing radiation from the decay of radioactive elements present within it, primarily uranium. For this reason, it is rarely observed in a fully crystalline form. ## Physical Properties Davidite-(La) has a hardness ranging from 5-6 on the Mohs scale. It exhibits a luster from pitchy to almost metallic, and an earthy or dull luster on weathered surfaces. It is an opaque mineral. Its density is high, approximately 4.42 g/cm³. Due to its metamict nature, it displays a very distinct conchoidal fracture. ## Colors and Varieties This mineral is typically black, sometimes with a brownish or grayish tint. The streak is black or grayish-black. No distinct color varieties or commercial varieties are recognized. ## History and Name The name "davidite" was given in honor of Tannatt William Edgeworth David (1858-1934), a Welsh-Australian geologist and explorer. The suffix "-(La)" indicates the dominance of lanthanum in a specific crystallographic site, in accordance with the naming conventions for minerals of the crichtonite group. The original davidite was described by Douglas Mawson in 1906, and davidite-(La) was formally defined as a distinct mineral species later. ## Uses Due to its rarity and often inconspicuous appearance, davidite-(La) is primarily of scientific and collector interest. It is sought after by collectors specializing in rare earth minerals and radioactive minerals.

Properties

Mohs hardness: 5-6
Luster: Resinous to metallic
Streak: Black
Density: 4.42
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features of davidite-(La) include its black color, pitchy luster, high density, conchoidal fracture, and strong radioactivity, easily detectable with a Geiger counter. It occurs in characteristic mineral associations. ## Distinguishing from Similar Minerals It can be confused with other black, heavy minerals such as ilmenite, magnetite, uraninite, or other minerals from the crichtonite group. It differs from ilmenite and magnetite by its lack of magnetic properties and strong radioactivity. It differs from uraninite often by its mode of occurrence and harder geological formation conditions (metamorphic rocks, pegmatites). Precise identification from other members of the crichtonite group (e.g., davidite-(Ce), crichtonite) requires advanced chemical analyses (EDS/WDS). ## Crystal Forms Crystals are rare, usually poorly formed, tabular in habit, often with a trigonal outline. Most commonly, it forms amorphous, granular, or massive aggregates within the host rock.

Geological environment

## Genesis Davidite-(La) is a mineral of hydrothermal or metamorphic origin. It forms under high-temperature conditions. It is most commonly found in hydrothermal veins cutting metamorphic rocks, as well as in skarns and some pegmatites. ## Mineral Associations It co-occurs with minerals such as rutile, ilmenite, hematite, titanite, allanite, quartz, feldspars, cordierite, as well as other rare earth minerals and uranium minerals. ## Localities The most important and classic localities for this mineral include Radium Hill in South Australia (the discovery site of the original davidite), the Tuva region in Siberia (Russia), where well-defined davidite-(La) was found, as well as some occurrences in Norway and the United States (e.g., California).

Rarity

Rare

For collectors

## Quality Criteria For collectors, specimens with well-formed, even if partially, crystals are most desirable, which is a great rarity. Specimens of large size, intense luster, and those solidly embedded in a contrasting rock matrix are also valued. Accurate chemical verification confirming it is davidite with lanthanum dominance is also important. ## Popular Localities Specimens from classic localities, such as Radium Hill in Australia or sites in Siberia, are particularly prized for their historical and scientific significance.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Avoid water and any chemical agents, as they can react with the mineral's surface, especially if it is weathered. ## What to Avoid As a radioactive mineral, it requires careful handling. Avoid inhaling dust that may be generated during processing or cleaning. Do not heat it, as this may alter its properties. Protect it from chemicals and moisture. ## Storage It is recommended to store specimens in separate, well-ventilated containers or display cases, away from other radiation-sensitive minerals. Clearly label it as radioactive. Store away from areas of constant human presence.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDavidite