Cardite

Chemical formula: Zn₂+₅.₅(As₅+O₄)₂(As₅+O₃OH)(OH)₃·₃H₂O

Cardite is a very rare zinc arsenate, forming colorless, hexagonal crystals, discovered in the Tsumeb mine in Namibia.

## Characteristics Cardite is a hydrated zinc arsenate, occurring as small, hexagonal, prismatic crystals. They are typically colorless and transparent, with a vitreous luster. Crystals rarely exceed 1 mm in length and often form radial aggregates or small, rosette-like clusters on the surface of other minerals. ## Physical Properties This mineral is characterized by a hardness of approximately 3 on the Mohs scale. It has a white streak and a vitreous luster. It is transparent to translucent. The calculated density is 4.14 g/cm³. ## History and Name Cardite was discovered in the famous Tsumeb mine in Namibia, known for its occurrence of many rare and unique minerals. It was described in 1999 by J. Keller, J. Innes, and G. Dunning. The mineral is named in honor of Dr. Walter Card, a Canadian mineral collector who first noticed the unusual specimen and submitted it for research. ## Uses Due to its extreme rarity and microscopic crystal size, Cardite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 4.14
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Amateur identification of Cardite is practically impossible. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS/WDS), due to its resemblance to other colorless arsenates from Tsumeb. ## Differentiation from similar minerals Cardite can be confused with many other rare, secondary minerals from Tsumeb, such as leiteite, köttigite, or prosopite. Differentiation is based on the analysis of crystal habit (hexagonal prisms) and confirmation of chemical composition and crystal structure in the laboratory. ## Crystal forms Cardite forms elongated, prismatic crystals with a hexagonal cross-section. Crystals are typically small, reaching up to 1 mm in length. They often occur as radial or rosette-like aggregates.

Geological environment

## Genesis Cardite is a secondary mineral that formed in the oxidation zone (gossan) of the polymetallic deposit in Tsumeb. It originated from the weathering of primary zinc and arsenic ores in a carbonate-rich environment, within dolomitic rocks. ## Mineral associations This mineral occurs in association with other rare arsenates and secondary minerals. It most commonly co-occurs with leiteite, zincite, smithsonite, tenorite, quartz, and unidentified zinc arsenates. ## Localities The only confirmed locality for Cardite in the world is the Tsumeb mine (31st level), in the Oshikoto region of Namibia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality criteria The most valuable Cardite specimens are those that possess well-formed, sharply terminated, and transparent crystals, forming aesthetic, radial aggregates. Association with other rare minerals from Tsumeb is also crucial, as it enhances the scientific and visual value of the specimen. Due to the microscopic nature of the mineral, the size of individual crystals and the richness of the aggregate are the most important factors. ## Popular localities The only source of Cardite specimens is the historic Tsumeb mine in Namibia. All specimens available on the collector's market originate from this single, classic locality.

Care and storage

## Cleaning Due to its extreme rarity and delicacy, Cardite specimens should be cleaned very carefully. Only gentle dust removal with a soft brush or a photographic air blower is recommended. Contact with water and any chemical agents should be avoided. ## What to avoid Ultrasonic cleaners, strong chemicals, acids, and bases should be absolutely avoided. The mineral is sensitive to changes in temperature and humidity. It should not be exposed to direct sunlight, which can cause damage. ## Storage Cardite specimens are best stored in stable conditions, in closed, padded "micromount" boxes that protect them from dust, mechanical damage, and sudden changes in humidity. Display should be in enclosed showcases with controlled lighting.

Sources

IMA Mineral List (CNMNC)