Lumsdenite

Chemical formula: NaCa₃Mg₂(As₃+V₄+₂V₅+₁₀As₅+₆O₅₁)·₄₅H₂O

Lumsdenite is a very rare, complex sodium, calcium, and magnesium arsenate-vanadate, forming microscopic, platy crystals of a blue-green color.

## Characteristics Lumsdenite is an extremely rare mineral from the arsenate and vanadate group, with a very complex chemical composition. It occurs as extremely small, platy or bladed crystals, rarely exceeding 50 micrometers in length. These crystals form rosette-like or spherulitic aggregates on the surface of the host rock. Due to its microscopic size, its visual characteristics are difficult to assess without specialized equipment. ## Physical Properties Lumsdenite crystals exhibit a luster described as vitreous to pearly. They are flexible and can be bent. Hardness and density have not been precisely measured due to the small amount of available material and the microscopic size of the crystals. ## Colors and Varieties This mineral is characterized by a vivid, blue-green color. No color varieties or commercial varieties have been observed, which is typical for such rare and newly discovered minerals. ## History and Name Lumsdenite was recognized as a new mineral species by the International Mineralogical Association (IMA) in 2015 (IMA2015-087). The name honors John S. Lumsden, an American mineral collector from the Calico Mountains area in California, who provided the samples on which the discovery was made. The mineral was described by a research team led by Anthony R. Kampf. ## Applications Lumsdenite has no industrial applications. Its significance is purely scientific and collectible, as a unique and extremely rare representative of the mineral world.

Properties

Luster: Vitreous to pearly
Streak: Pale green
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Field identification of lumsdenite is impossible. Identification relies on laboratory analysis combined with its characteristic appearance under a microscope: blue-green, rosette-like aggregates of very small, platy crystals. The key factors are the locality (Cole Mine) and co-occurrence with other rare arsenates. ## Distinguishing from Similar Minerals Lumsdenite can be confused with other secondary, colored arsenic and vanadium minerals found in the same environment, such as ewingite, fianelite, or hughesite. Definitive differentiation requires advanced analytical techniques, such as X-ray diffraction (XRD) and chemical analysis (EDS), due to similarities in color and micro-scale form. ## Crystal Forms Lumsdenite forms thin, platy crystals with a hexagonal outline, elongated in one direction. These crystals combine into characteristic, rosette-like or spherulitic (radiating) aggregates that densely cover the rock surface.

Geological environment

## Genesis Lumsdenite is a secondary mineral, formed by weathering processes in desert conditions. It forms as an oxidation product of ore minerals (mainly arsenopyrite) in arsenic- and vanadium-rich lake sediments that have undergone hydrothermal processes. It occurs as coatings and crusts on rock surfaces in the weathering zone. ## Mineral Associations This mineral occurs in paragenesis with other rare, secondary arsenates and vanadates. It is most often accompanied by: gypsum, celestine, fianelite, hughesite, ewingite, adamsite-(Y), and the newly discovered leószilárdite. ## Localities The only confirmed occurrence of lumsdenite in the world is its type locality – the Cole Mine (Shaft No. 2), located in the Calico Mountains in San Bernardino County, California, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a lumsdenite specimen is assessed based on the richness and coverage of the rock surface by microcrystalline aggregates. The most desirable samples are those with dense, well-formed rosettes of intense, blue-green color, contrasting with the rock matrix. The size of individual crystals, although always microscopic, also influences the evaluation – larger and better-formed plates are more highly valued. The presence of interesting associated minerals is also important. ## Popular Localities The only source of lumsdenite specimens is its type locality – the Cole Mine in California, USA. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Lumsdenite specimens should absolutely not be cleaned. Any attempt at cleaning, even with water, can destroy or remove the microscopic crystals from the rock surface. The mineral should be treated solely as an observational object. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any touching or rubbing. The crystals are extremely delicate and fragile. Protect the specimen from dust and sudden temperature changes. ## Storage Lumsdenite specimens should be stored exclusively in sealed, transparent "micromount" containers or membrane boxes. This protects the delicate crystals from mechanical damage, dust, and moisture, while allowing for safe observation.

Sources

IMA Mineral List (CNMNC)