Botallackite

Chemical formula: Cu²⁺₂Cl(OH)₃

Botallackite is a rare polymorph of atacamite, forming thin, platy crystals of a characteristic blue-green color.

## Characteristics Botallackite is a rare secondary copper mineral, belonging to the polymorphous group of atacamite, meaning it has the same chemical composition (Cu₂Cl(OH)₃) but a different crystal structure. It occurs as very small, thin, platy or bladed crystals, rarely exceeding 1 mm in length. These crystals often form rosette aggregates, crusts, or thin veins. Due to its delicate nature and small size, it is a mineral primarily valued by specialized collectors. ## Physical Properties This mineral is characterized by a vitreous luster and is typically translucent. It exhibits perfect cleavage in one direction, which is visible in larger crystals. Its Mohs hardness is approximately 3, and its density ranges from 3.60 to 3.62 g/cm³, which is typical for secondary copper minerals. ## Colors and Varieties Botallackite occurs in characteristic shades from turquoise-blue and pale blue to blue-green. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from its first discovery location – the Botallack Mine in Cornwall, United Kingdom. It was first described by Arthur H. Church in 1865. The type locality is known for the occurrence of many rare secondary copper and tin minerals. ## Uses Botallackite has no industrial application. Its significance is purely scientific and as a collector's item.

Properties

Mohs hardness: 3
Color: Mountain-green, bluish green to green; pale bluish green in transmitted light
Luster: Vitreous
Streak: Pale green
Density: 3.6
Cleavage: In one direction perpendicular to Z axis
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Botallackite can be identified by its characteristic blue-green color, thin, platy crystals often forming rosette aggregates, and its occurrence in the oxidation zones of copper deposits. It is a secondary mineral, usually found in small quantities on other minerals. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals such as atacamite, paratacamite, clinoatacamite, or spangolite. Atacamite and paratacamite typically form prismatic or granular crystals, in contrast to the thin plates of botallackite. Spangolite has a similar color but crystallizes in the trigonal system, forming different crystal habits. Final differentiation from its polymorphs often requires advanced analytical methods (e.g., XRD). ## Crystal Habits Crystals are usually very small, thin, platy or bladed, and flattened. They often occur as radiating or rosette aggregates, as well as thin crusts and coatings.

Geological environment

## Genesis Botallackite is a secondary mineral, forming in the oxidation zones (gossans) of copper deposits, especially in chloride-rich environments, such as coastal areas. It forms as a result of saltwater acting on primary copper minerals. It can also form on ancient metallurgical slags submerged in seawater. ## Mineral Associations It often co-occurs with other secondary copper minerals such as atacamite, paratacamite, clinoatacamite, malachite, as well as cuprite, tenorite, calcite, and quartz. ## Localities The most important localities worldwide include the historical type locality – the Botallack Mine in Cornwall (United Kingdom). Other known occurrences include the Lizard Peninsula in Cornwall, mines in the Lavrion area in Greece, the Atacama Desert in Chile, and some localities in Arizona (USA) and Saxony (Germany).

Rarity

Rare

For collectors

## Quality Criteria The most prized botallackite specimens are characterized by well-formed, sharp crystals with an intense blue or blue-green color. Rich rosette aggregates on a contrasting rock matrix are highly valued. Due to the small size of the crystals, specimens are usually "micromount" type, and their value increases with the size and aesthetics of the crystals. ## Popular Localities Classic and most desirable specimens come from historical mines in Cornwall, especially Botallack and Levant. Specimens from Lavrion, Greece, are also valued by collectors.

Care and storage

## Cleaning Botallackite specimens are extremely delicate and sensitive. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust. Water should be avoided, especially ultrasonics and steam cleaners, which will destroy the specimen. ## What to Avoid The mineral is sensitive to chemicals, including acids and ammonia. Sudden temperature changes and prolonged exposure to strong light, which can cause fading, should be avoided. Botallackite is unstable in low humidity conditions and may dehydrate or transform into other, more stable minerals, such as atacamite. ## Storage It is recommended to store specimens in closed, padded collector boxes (so-called "micromount boxes") to protect them from mechanical damage, dust, and humidity fluctuations. Display should be in stable conditions, away from direct sunlight and heat sources.