Hydrombobomkulite

Chemical formula: (Ni₂+,Cu₂+)Al₄(N₅+O₃,S₆+O₄)₂(OH)₁₂·₁₄H₂O

Hydrombobomkulite is an extremely rare, blue-green hydrated nickel, copper, and aluminum sulfate and nitrate, closely related to mbobomkulite.

## Characteristics Hydrombobomkulite is a very rare secondary mineral, occurring as microscopic, spherulitic aggregates and rosettes. Its crystals form thin, platy lamellae with a hexagonal outline, reaching up to 0.1 mm in size. Due to the small size of the crystals, its visual features are difficult to observe without specialized equipment. ## Physical Properties This mineral is characterized by a vitreous or waxy luster. It is very soft, with a Mohs hardness of only 1-2. It is a light mineral, with a calculated density of 2.31 g/cm³. Individual crystals are flexible. ## Colors and Varieties Hydrombobomkulite has a characteristic blue-green color. No varieties have been distinguished. ## History and Name The mineral's name refers to its chemical composition (hydrated form) and its close relationship to mbobomkulite. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1992. It was described by T. Witzke and U. Kolitsch in 2000 based on material from the Saalfeld mine in Thuringia, Germany.

Properties

Mohs hardness: 1-2
Luster: Vitreous
Streak: Pale blue-green
Density: 2.31
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identification of hydrombobomkulite is possible only through advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Visually, it is practically impossible to distinguish from other similar secondary minerals without specialized magnification and knowledge. ## Distinguishing from Similar Minerals It can be confused with the closely related mbobomkulite, from which it differs by a higher water content in its structure. Distinguishing these two minerals requires crystallographic analysis. It can also be confused with other secondary copper and nickel sulfates and nitrates, such as niedermayrite. ## Crystal Forms It forms microscopic, spherulitic aggregates, rosettes, or spherical clusters composed of very small, thin, platy crystals with a hexagonal outline.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones of ore deposits. It forms as a result of the weathering of primary minerals containing nickel, copper, and sulfides in the presence of organic matter (e.g., oil shale), which is a source of nitrates. ## Mineral Associations It co-occurs with other secondary minerals, such as mbobomkulite, gypsum, chalcanthite, epsomite, retgersite, morenosite, as well as with host rock minerals like quartz and calcite. ## Localities Its occurrence has been confirmed in only a few places worldwide. The most important of these are the type locality in the alum shale mines in the Saalfeld area in Thuringia (Germany) and in the Lichtenberg Absetzer mine near Ronneburg, also in Thuringia. It is also known from the Příbram mine in the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, its collector value primarily depends on the richness and aesthetics of the microscopic aggregates on the rock matrix. Specimens with well-formed, abundant spherulites of intense, blue-green color, contrasting with the substrate, are most highly valued. Precise documentation and confirmation of the mineral's identification are also crucial. ## Popular Localities The most known and valued specimens, which are also the type material, come from the historic mines in the Saalfeld area in Thuringia, Germany.

Care and storage

## Cleaning Due to its extreme rarity, small size, and delicacy, hydrombobomkulite specimens are practically not subject to cleaning. Any attempts at mechanical or chemical cleaning can irreversibly destroy the mineral. It should be left intact on the host rock. ## What to Avoid Avoid contact with water, chemicals, as well as any vibrations and impacts. The mineral is very soft and sensitive to changes in humidity and temperature. It should not be heated or exposed to ultrasound. ## Storage Specimens should be stored exclusively in specialized, sealed "micromount" containers, protecting them from dust, moisture, and mechanical damage. Store in stable room conditions, away from heat and light sources.

Sources

IMA Mineral List (CNMNC)