Thérèsemagnanite

Chemical formula: NaCo₂+₄(S₆+O₄)(OH)₆Cl·₆H₂O

A rare, hydrated sodium cobalt sulfate with an intense pink color, occurring as microscopic, tabular crystals.

## Characteristics Thérèsemagnanite is a very rare mineral from the sulfate group, chemically classified as a hydrated sodium cobalt sulfate with additional hydroxyl and chloride ions. It occurs as extremely small, thin, tabular crystals with a hexagonal outline, rarely exceeding 0.1 mm. These crystals form rosette-like aggregates, thin coatings, or crusts on the surface of the host rock. Due to its microscopic size, it is a mineral primarily accessible to specialized collectors and scientific institutions. ## Physical Properties The crystals are too small to reliably determine their hardness or density using standard methods. They exhibit a vitreous luster. They are transparent to translucent. ## Colors and Varieties The mineral is characterized by an intense, pinkish-red color. No varieties have been distinguished. ## History and Name The mineral is named in honor of Thérèse Magnan (born 1950), a French mineral collector from Cap Garonne, who discovered the first specimens of this mineral. It was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1993. The type locality is the Cap Garonne mine in Le Pradet, Var, France. ## Uses Thérèsemagnanite has no industrial applications. Its significance is purely scientific and collectible.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Light pink
Density: 2.61
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of thérèsemagnanite under amateur conditions is practically impossible. Key features include its intensely pinkish-red color, occurrence as microscopic, hexagonal tabular crystals forming rosette-like aggregates, and co-occurrence with other rare secondary minerals in the oxidation zones of polymetallic deposits. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with other pink or red secondary minerals, such as erythrite or spherocobaltite. Erythrite typically forms acicular or prismatic crystals, while spherocobaltite forms spherical aggregates. Final distinction is only possible based on chemical and crystallographic analysis. ## Crystal Forms It forms very small, thin, tabular crystals with a hexagonal outline. These crystals often combine into rosette-like or fan-shaped aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis Thérèsemagnanite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic deposits rich in cobalt and arsenic. It forms as a result of the reaction of ore-forming waters with primary minerals in a chloride-rich environment. At the type locality (Cap Garonne), it formed through the weathering processes of old mining dumps. ## Mineral Associations It most commonly co-occurs with other rare secondary minerals. At the Cap Garonne mine, it has been found in association with erythrite, kankite, pitticite, geminite, lavendulan, and gillardite. ## Localities This is an extremely rare mineral, known from only a few localities worldwide. The most important and also the type locality is the former copper and lead mine of Cap Garonne in Le Pradet, Var, France. Additionally, its presence has been reported in the Bouismas mine in Morocco and the Dolores mine in Spain.

Rarity

Very rare

For collectors

## Quality Criteria The quality of thérèsemagnanite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates on the rock matrix. Specimens with well-formed, intensely colored crystal rosettes, contrasting well with the substrate, are most highly valued. Due to the microscopic nature of the mineral, the quality of the specimen under a microscope is also crucial. The presence of rare associated minerals increases its scientific and collectible value. ## Popular Localities By far the most known and valued specimens come from the type locality – the Cap Garonne mine in France. Material from this location serves as the standard for the species.

Care and storage

## Cleaning Specimens should be handled with the utmost care. Due to the microscopic size and delicacy of the crystals, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Avoid contact with water, which can dissolve or damage the mineral. ## What to Avoid Absolutely avoid contact with water, acids, detergents, and other chemicals. The mineral is likely sensitive to changes in humidity and high temperatures. It should not be heated or exposed to direct sunlight. ## Storage It is recommended to store specimens in stable conditions, in closed, airtight containers (e.g., "micromount boxes"), to protect them from dust, mechanical damage, and humidity fluctuations.

Sources

IMA Mineral List (CNMNC)