Cyanotrichite

Chemical formula: Cu²⁺₄Al₂S⁶⁺O₄(OH)₁₂·₂H₂O

Cyanotrichite is a hydrated copper and aluminum sulfate, forming characteristic, acicular crystals of an intensely blue color.

## Characteristics Cyanotrichite is a secondary mineral from the sulfate group, valued for its unique appearance. It forms aggregates of fine, acicular or fibrous crystals, which often arrange themselves into radial aggregates, rosettes, or velvety coatings on the host rock. Individual crystals are usually too small to be seen with the naked eye, but their dense clusters give specimens a fluffy, silky texture. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2. The crystals are brittle and delicate. The luster is silky, especially noticeable in dense aggregates. It is a translucent to transparent mineral in the case of individual, microscopic crystals. ## Colors and Varieties Cyanotrichite is characterized by a vivid blue color, ranging from sky-blue to azure-blue. The name of the mineral directly refers to its color and form. No color varieties or commercial varieties are distinguished. ## History and Name The name cyanotrichite comes from the Greek words *kyanos* (κυανός) meaning "blue" and *thrix* (θρίξ) meaning "hair," which is an apt description of its appearance. The mineral was first described in 1839 by the German mineralogist Ernst Friedrich Glocker. ## Uses Due to its rarity, small crystal size, and delicacy, cyanotrichite has no industrial applications. However, it is a highly valued and sought-after collector's stone.

Properties

Mohs hardness: 1-3
Color: Sky-blue, azure-blue
Luster: Silky
Streak: Light blue
Density: 2.76
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Cyanotrichite is relatively easy to identify due to its characteristic form of occurrence – velvety or fluffy coatings and radial aggregates of tiny, acicular crystals. Its intensely blue color and silky luster are also key diagnostic features. It reacts with hydrochloric acid, releasing gas bubbles. ## Distinguishing from Similar Minerals Cyanotrichite is sometimes confused with other secondary blue copper minerals. - **Aurichalcite**: Has a similar form of acicular coatings, but its color is usually lighter, more sky-blue or greenish-blue. Aurichalcite is a carbonate and also reacts with acids. - **Brochantite**: Often forms similar acicular aggregates, but its color is usually darker, emerald-green, not blue. - **Linarite**: Has an intense azure color, but usually forms better-developed, tabular or prismatic crystals, rather than acicular aggregates. ## Crystal Forms Crystals are strongly elongated, acicular or fibrous. They almost always occur as dense aggregates, forming radial aggregates, spherical forms, fluffy coatings, and crusts resembling velvet.

Geological environment

## Genesis Cyanotrichite is a secondary mineral, forming in the oxidation (weathering) zones of copper ore deposits. It forms as a result of surface waters acting on primary copper sulfides, in the presence of aluminum minerals. It is a typical mineral of the supergene zone. ## Mineral Associations It often co-occurs with other secondary copper minerals and sulfates. The most common associated minerals include: brochantite, malachite, azurite, spangolite, chalcophyllite, olivenite, tyrolite, as well as gypsum and limonite. ## Localities Significant specimens come from several locations worldwide. In the USA, beautiful specimens have been found in the Grandview Mine in Arizona and in mines in Utah. In Europe, it is known from Laurion in Greece, Cap Garonne in France, and Romania (Moldova Nouă). Other known localities include Sichuan Province in China and Tsumeb in Namibia.

Rarity

Not very common

For collectors

## Quality Criteria The most highly valued cyanotrichite specimens are characterized by an intense, azure color and a large coverage area on the host rock. Well-formed, radial aggregates ("sunbursts") or dense, velvety coatings without damage enhance their attractiveness. Contrast with a light host rock (e.g., quartz) is also desirable. The size of individual needles, though always small, also affects the value – the longer they are, the more interesting the specimen. ## Popular Localities Specimens from the Grandview Mine in Arizona (USA), which often show beautiful contrast with white rock, are considered classic and most sought-after. In recent years, spectacular specimens from mines in Sichuan Province in China, characterized by large, rich coatings of vivid color, have dominated the market.

Care and storage

## Cleaning Cyanotrichite specimens are extremely delicate and sensitive. Cleaning should be kept to an absolute minimum. Only very careful removal of dust with a soft brush or a stream of compressed air from a distance is permissible. Contact with water is not recommended, as the mineral is soluble in it. ## What to Avoid Absolutely avoid contact with water (including distilled water), any chemicals, acids, and detergents. Ultrasonic cleaners are not recommended. The mineral is sensitive to high temperatures and direct, prolonged exposure to sunlight, which can cause it to fade. It should be protected from moisture and sudden temperature changes. ## Storage Specimens should be stored in closed, dry containers or display cases, away from light sources and dust. Due to its fragility, it should be protected from vibrations and impacts. It is best to store it in its original collector's box (a "membrane box") or another container that prevents the delicate needles from coming into contact with any surface.