Gobelinite

Chemical formula: Co²⁺Cu²⁺₄(S⁶⁺O₄)₂(OH)₆·6H₂O

Gobelinite is a very rare hydrated cobalt and copper sulfate, forming characteristic, sky-blue, spherical aggregates.

## Characteristics Gobelinite is a hydrated hydroxyl sulfate of cobalt and copper, belonging to the ktenasite group. It occurs as small, spherical or hemispherical aggregates with a radial internal structure, reaching up to 0.5 mm in diameter. Individual crystals forming the aggregates are thin, bladed or acicular. ## Physical properties Gobelinite crystals are flexible. Hardness on the Mohs scale is low, approximately 2. This mineral has a vitreous to pearly luster on cleavage surfaces. It is transparent to translucent. ## Colors and varieties Gobelinite is characterized by a light blue to sky-blue color. No varieties have been distinguished. ## History and name The mineral's name comes from the St. Joseph mine (also known as "Glücksstern") in the locality of GOBELin, in the municipality of Lahnstein, Rhineland-Palatinate, Germany, which is its type locality. Gobelinite was approved as a new mineral by the International Mineralogical Association (IMA) in 2011 (IMA2011-016). It was described by a team of mineralogists: N. V. Chukanov, I. V. Pekov, D. A. Varlamov, D. I. Belakovskiy, S. N. Britvin, and A. Schüller.

Properties

Mohs hardness
2.5
Color
Pale green, bluish green, greyish green
Luster
Vitreous
Streak
White (with a pale-green cast)
Density
2.95
Cleavage
Perfect on {100}
Fracture
Irregular/Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Gobelinite can be identified by its characteristic mode of occurrence – small, spherical aggregates of sky-blue color and radial internal structure. A light blue streak is also a helpful feature. ## Distinguishing from similar minerals It can be confused with other secondary copper sulfates of similar color and form, such as ktenasite, niedermayrite, or serpierite. Differentiation requires advanced analytical methods, such as chemical analysis (EDS/WDS) to confirm the presence and proportions of cobalt and copper, and X-ray diffraction (XRD) to verify the crystal structure. ## Crystal forms It forms spherical or hemispherical aggregates up to 0.5 mm in diameter, composed of radially arranged, thin crystals with a bladed or acicular habit, elongated along the [001] axis.

Geological environment

## Genesis Gobelinite is a secondary mineral, formed in the oxidation (supergene) zones of polymetallic ore deposits. It forms as a result of the weathering of primary minerals containing copper and cobalt, under conditions of low temperature and pressure. ## Mineral associations At its type locality in Germany, it co-occurs with chalcopyrite, tetrahedrite, galena, barite, quartz, niedermayrite, and serpierite. ## Localities The only confirmed locality for gobelinite in the world is its type locality – the former St. Joseph mine (Glücksstern Mine) in GOBELin, Lahnstein, in the Taunus Mountains, Rhineland-Palatinate, Germany.

Rarity

Extremely rare

For collectors

## Quality criteria As a mineral of purely scientific and collector interest, specimens with well-formed, undamaged spherical aggregates, clearly contrasting with the host rock, are most valued. The size of the aggregates and the intensity of the color also affect the specimen's value. Due to their microscopic size, specimens are usually evaluated under magnification.

Care and storage

## Cleaning Due to its extreme rarity, low hardness, and solubility in acids, mechanical or chemical cleaning is absolutely inadvisable. Specimens should be protected from dust and contaminants. ## What to avoid Avoid contact with water, chemicals (especially acids), ultrasound, and sudden temperature changes. The mineral is sensitive to dehydration, so it should not be stored in an overly dry environment or exposed to direct sunlight or strong lighting that could heat it. ## Storage Gobelinite specimens should be stored under stable conditions, preferably in closed, padded collector boxes or special display cases with controlled humidity. They should be protected from vibrations and mechanical damage.

External references

Sources

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