Schulenbergite

Chemical formula: (Cu²⁺,Zn²⁺)₇(S⁶⁺O₄)₂(OH)₁₀·₃H₂O

Schulenbergite is a rare, secondary copper and zinc mineral, forming characteristic, rosette-like aggregates of light blue or blue-green color.

## Characteristics Schulenbergite is a hydrated copper and zinc hydroxyl sulfate. It occurs as very small, tabular or platy crystals, which almost always form spherical or rosette-like aggregates. Individual crystals are rarely visible to the naked eye, and specimens most often appear as thin, delicate crusts and coatings on the host rock. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2. Crystals exhibit perfect cleavage in one direction, which, combined with their small size, makes them extremely brittle. The luster is described as pearly, especially visible on cleavage surfaces. It is a transparent mineral with a density of 3.28 g/cm³. ## Colors and Varieties Schulenbergite ranges in color from light blue to blue-green. Its hue is characteristic and often serves as the first clue for identification. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral was first described in 1984. Its name comes from its discovery locality – the Oberschulenberg area near Clausthal-Zellerfeld in Lower Saxony (Germany), where its type locality (Glücksrad mine) is located.

Properties

Mohs hardness: 2
Luster: Pearly
Streak: Pale blue-green.
Density: 3.28
Cleavage: Perfect on {0001}; poor on <mi>{11_20}</mi>
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification The key diagnostic feature of schulenbergite is its mode of occurrence – spherical or rosette-like aggregates composed of tiny, tabular crystals. Its characteristic light blue to blue-green color, pearly luster, and very low hardness are also distinctive. ## Distinguishing from Similar Minerals Schulenbergite is sometimes confused with other secondary copper minerals of similar color and form, such as aurichalcite, rosasite, or brochantite. Aurichalcite and rosasite tend to form acicular or fibrous aggregates and react with hydrochloric acid. Brochantite usually occurs as acicular or prismatic crystals with a darker, green color. ## Crystal Forms Crystals are hexagonal, very thin, and tabular. They almost always occur as spherical or hemispherical aggregates with a radial internal structure, as well as rosettes and thin crusts.

Geological environment

## Genesis Schulenbergite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic ore deposits rich in copper and zinc. It forms as a result of surface water acting on primary sulfides, such as chalcopyrite and sphalerite, in voids and fissures of rocks. ## Mineral Associations It often co-occurs with other secondary minerals of the oxidation zone. The most common associations include: gypsum, brochantite, linarite, anglesite, cerussite, malachite, azurite, goethite, and covellite. ## Localities The most important occurrences of this mineral are found in Germany (Harz Mountains, Black Forest), Greece (Lavrion mines), Great Britain (Cumbria, Cornwall), Austria, Italy (Sardinia), and the USA (Arizona, Nevada).

Rarity

Rare

For collectors

## Quality Criteria The most prized schulenbergite specimens are those with well-formed, spherical aggregates of intense blue color, contrasting with the color of the host rock. The absence of damage to the delicate spherulites, as well as the size and abundance of the occurrence on the specimen, are important. Due to the small size of its crystals, it is a mineral valued mainly by collectors specializing in microminerals. ## Popular Localities Classic and most sought-after specimens come from the type locality in Germany (Glücksrad mine, Oberschulenberg) and from historical mines in the Lavrion region of Greece, which yield specimens with exceptionally aesthetic, blue spheres.

Care and storage

## Cleaning Schulenbergite specimens are extremely delicate and brittle. They should be cleaned only very carefully, using compressed air to remove dust. Any contact with water, and especially with a brush, risks irreversible damage to the fragile aggregates. ## What to Avoid Avoid contact with water and all chemicals, including acids, which can dissolve it. The mineral is sensitive to shocks and mechanical damage. It should not be heated or exposed to prolonged moisture. ## Storage Specimens should be stored in closed, stable containers (so-called micromineral boxes) to protect them from dust, moisture, and mechanical damage. Due to its fragility, it is not suitable for display without such protection.

External references

https://www.mindat.org/min-3589.html