Zilbermintsite-(La)

Chemical formula: (CaLa₅)(Fe³⁺Al₃Fe²⁺)[Si₂O₇][SiO₄]₅O(OH)₃

Zilbermintsite-(La) is a very rare mineral from the epidote group, discovered in Israel, distinguished by its complex chemical composition with lanthanum as the dominant rare earth element.

## Characteristics Zilbermintsite-(La) is a mineral belonging to the allanite subgroup within the epidote group. It occurs as anhedral (lacking crystal faces) grains up to 200 micrometers in size, forming aggregates with other minerals. It is opaque, black in color, and has a resinous luster. Its uniqueness lies in its complex chemical composition, in which lanthanum is the dominant rare earth element, as indicated by the -(La) suffix in its name. ## Physical Properties This mineral is characterized by a Mohs hardness of 6-7, making it relatively hard. Its density, calculated from crystallographic data, is 4.41 g/cm³. It has a resinous luster and a black streak. It does not exhibit cleavage, and its fracture is uneven. ## Colors and Varieties Zilbermintsite-(La) is a mineral of uniform black color. No color varieties or commercial varieties are known. ## History and Name The mineral's name honors Professor Mikhail V. Zilbermint (born 1959), a Russian mineralogist and crystallographer, for his contributions to the study of minerals from the Hatrurim Formation in Israel. The -(La) suffix indicates lanthanum as the dominant rare earth element in its composition. The mineral was approved by the International Mineralogical Association (IMA) in 2021 (IMA2021-091), and its description was published in 2023. The type locality (locus typicus) is the Nabi Musa deposit in the Hatrurim Complex in the Judean Desert, Israel. ## Applications Due to its extreme rarity and microscopic size, Zilbermintsite-(La) has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized systematic and micromineral collections.

Properties

Mohs hardness
6-0
Color
light brown
Luster
Resinous
Streak
brown
Density
4.684
Cleavage
One direction of good cleavage and one direction of imperfect cleavage were observed under the scanning electron microscope. Assume that good cleavage could be on {100}
Fracture
Irregular/Uneven,Step-Like
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of Zilbermintsite-(La) is impossible without advanced analytical techniques. This requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm its complex composition with dominant lanthanum, and X-ray diffraction (XRD) to determine its crystal structure. Visually, it is a black, resinous mineral occurring as microscopic grains. ## Distinguishing from Similar Minerals It can be confused with other black minerals from the epidote group, such as allanite-(Ce) or allanite-(La), as well as other dark minerals found in the Hatrurim Formation. Definitive differentiation is possible only through detailed chemical analysis, which will reveal unique elemental proportions, including the dominance of lanthanum and specific cation occupancy. ## Crystal Forms This mineral has only been found in the form of anhedral (irregular, without developed faces) grains, which form aggregates with other minerals of the host rock.

Geological environment

## Genesis Zilbermintsite-(La) forms under specific conditions of pyrometamorphic metamorphism. It was discovered in a rock called paralarnite, which is a product of high-temperature (above 800°C) alteration of marly rocks. This process occurs in the Hatrurim Formation in Israel, known for the occurrence of rare minerals formed by the natural combustion of bitumens. ## Mineral Associations This mineral co-occurs with other products of pyrometamorphism. At the type locality, it was found in association with minerals such as brownmillerite, mayenite, ye'elimite, larnite, fluorapatite, magnetoferrite, maghemite, hematite, and members of the perovskite group. ## Localities The only confirmed locality of Zilbermintsite-(La) in the world is its type locality: the Nabi Musa deposit, in the Hatrurim Basin, Judean Desert, West Bank, Israel.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, the collector value of Zilbermintsite-(La) is not assessed based on typical criteria such as size or color. The most valuable specimens are those where the mineral grains are clearly visible, abundant, and well-identified analytically. Association with other rare minerals from the Hatrurim Formation and accurate documentation confirming the mineral's identity are crucial. ## Popular Localities The only source of specimens is the type locality in Israel. Material from this location is extremely difficult to obtain and primarily goes to scientific institutions and highly specialized micromineral collectors.

Care and storage

## Cleaning Specimens of this mineral, typically microscopic grains within the host rock, do not require cleaning. Any attempt at mechanical or chemical cleaning may irreversibly damage the mineral. ## What to Avoid Avoid contact with any chemicals, acids, and bases. Ultrasound and sudden temperature changes are not recommended. Protect the specimen from abrasion and mechanical damage. ## Storage Micromineral specimens, such as Zilbermintsite-(La), should be stored in specialized, sealed "micromount" boxes that protect them from dust and damage. Avoid exposure to moisture and direct sunlight, although there is no evidence of its particular sensitivity to light.

External references

Sources

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