Redgillite

Chemical formula: Cu²⁺₆S⁶⁺O₄(OH)₁₀·H₂O

Redgillite is a rare, hydrated copper hydroxyl sulfate, forming microscopic, tabular crystals of an intense green color.

## Characteristics Redgillite is a rare secondary mineral from the sulfate group, chemically classified as a hydrated copper hydroxyl sulfate. It occurs as very small, thin, tabular crystals, rarely exceeding 1 mm in length. These crystals often form rosette-like or spherical aggregates, as well as coatings and efflorescences on other minerals. Due to the small size of the crystals, its features are most often observed under magnification. ## Physical Properties This mineral is characterized by low hardness, measuring 2 on the Mohs scale, which makes it very delicate. Its density, calculated based on the chemical formula and unit cell parameters, is 3.45 g/cm³. The crystals exhibit a vitreous luster and are transparent to translucent. It possesses good cleavage in three directions. ## Colors and Varieties Redgillite occurs in various shades of green – from light green, through grass-green and emerald-green, to nickel green. No named varieties are distinguished. ## History and Name Redgillite was first described in 1989. Its name comes from its discovery locality – the Red Gill mine in the Caldbeck Fells area, Cumbria, England. This is its type locality. ## Uses Due to its rarity and microscopic crystal size, redgillite has no industrial application. It is solely of scientific and collectible interest, being a prized micromineral.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
3.45
Cleavage
On {001}, good on {100} and {010}.
Fracture
Irregular/Uneven
Transparency
Transparent,Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Redgillite is identified by its characteristic form – small, thin, tabular crystals, often gathered in rosette-like aggregates. Key features also include its intense green color, low hardness, and co-occurrence with other secondary copper minerals in oxidation zones. ## Distinguishing from Similar Minerals Redgillite can be confused with other green, secondary copper minerals, such as brochantite, malachite, or niedermayrite. Distinguishing it from niedermayrite, to which it is closely related, is particularly difficult and often requires advanced analyses, such as X-ray diffraction (XRD). It differs from malachite by the absence of a reaction with hydrochloric acid, and from brochantite by subtle differences in hue and crystal form. ## Crystal Forms It forms very thin, lath-like or tabular crystals with a hexagonal outline. These crystals often combine into small, rosette-like or radial aggregates, and also form thin efflorescences and coatings.

Geological environment

## Genesis Redgillite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic ore deposits, mainly copper. It forms as a result of the weathering of primary copper sulfides in the presence of sulfate-rich waters. ## Mineral Associations This mineral often co-occurs with other secondary copper and lead minerals. Its most common associations include: brochantite, langite, anglesite, cerussite, chalcanthite, linarite, malachite, niedermayrite, and sporadically gypsum and quartz. ## Localities The most important and type locality for redgillite is the Caldbeck Fells area in Cumbria, England (Red Gill and Silver Gill mines). It is also known from several other localities worldwide, including the Clara mine in the Black Forest (Germany) and Laurion in Greece.

Rarity

Very rare

For collectors

## Quality Criteria The quality of redgillite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most valued are specimens with clearly formed, undamaged, rosette-like clusters of an intense, emerald-green color. Contrast with the rock matrix and the presence of rare associated minerals are also important. ## Popular Localities By far the most prized and classic redgillite specimens come from its type locality in Caldbeck Fells, Cumbria, England. Specimens from this region are considered exemplary for this species and fetch the highest prices in the micromineral collector's market.

Care and storage

## Cleaning Redgillite specimens should be cleaned with the utmost care, exclusively using compressed air to remove dust. Due to its extreme delicacy and small crystal size, any mechanical contact, including with brushes or water, should be avoided. ## What to Avoid The mineral is very soft (hardness 2), so touching, rubbing, and any vibrations should be avoided. It should be protected from chemicals, especially acids, which can damage it. It should not be exposed to high temperatures or ultrasound. ## Storage Redgillite should be stored in specialized micromount boxes, which protect it from dust, mechanical damage, and sudden changes in humidity. Exposure to direct sunlight, which could cause fading over time, should be avoided.

External references

Sources

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