Clinotyrolite
Chemical formula: Ca<sub>2</sub>Cu<sub>9</sub>(AsO<sub>4</sub>,SO<sub>4</sub>)<sub>4</sub>(OH,O)<sub>10</sub>·10H<sub>2</sub>O
Clinotyrolite is a very rare, secondary copper and arsenic mineral, forming characteristic blue-green aggregates with a pearly luster.
Properties
- Mohs hardness
- 1.5
- Luster
- Pearly
- Streak
- Pale blue
- Density
- 3.25
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Clinotyrolite is identified by its characteristic mode of occurrence – rosette-like or fan-shaped aggregates composed of tiny, bladed crystals. Key features also include its blue-green color, very low hardness (it can be scratched with a fingernail), and distinct pearly luster on cleavage planes. ## Distinguishing from Similar Minerals Clinotyrolite is visually almost identical to tyrolite. Reliable differentiation of these two minerals is possible almost exclusively using advanced analytical methods, such as X-ray diffraction (XRD), which allows for determining differences in their crystal systems (tyrolite is orthorhombic, clinotyrolite is monoclinic). It can also be confused with other secondary copper arsenates, such as agardite or mixite, which, however, usually form acicular or fibrous aggregates with a silky or vitreous luster, rather than pearly. ## Crystal Forms It forms very small, flattened, bladed crystals, elongated along the [100] axis. These crystals almost always occur as fan-shaped, spherical, or rosette-like aggregates.
Geological environment
## Genesis Clinotyrolite is a secondary mineral, forming in the oxidation zones of polymetallic ore deposits rich in copper and arsenic. It forms as a result of the weathering of primary copper sulfides and arsenides in the presence of waters rich in sulfates and calcium carbonates. ## Mineral Associations It most often co-occurs with minerals such as tyrolite, baryte, fluorite, quartz, malachite, azurite, olivenite, chalcophyllite, and other rare secondary arsenates. ## Localities The most important and well-documented occurrences of this very rare mineral are: - Germany: Clara Mine, Wolfach, Black Forest (type locality). - USA: Gold Hill Mine, Tooele County, Utah. - Slovakia: Nováky, Trenčín region.
Rarity
Very rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, distinct rosette-like or fan-shaped aggregates, with an intense, blue-green color. Contrast with the rock matrix (e.g., with white baryte or quartz) and absence of mechanical damage to delicate structures are important. Due to the microscopic size of the crystals, the size of the entire aggregate is crucial for the specimen's value. ## Popular Localities By far the most sought-after specimens come from the type locality – the Clara mine in Germany, which has provided the best quality clinotyrolite samples. Specimens from the Gold Hill mine in Utah are also valued in collections.
Care and storage
## Cleaning Clinotyrolite specimens are extremely delicate and sensitive. Mechanical cleaning should be avoided. If absolutely necessary, a stream of compressed air from a safe distance can be used to remove dust. Contact with water, especially warm water, can damage or dissolve the mineral. ## What to Avoid Contact with water, acids, ammonia, and other chemicals must be strictly avoided. The mineral is very soft, susceptible to scratches and mechanical damage. It should be protected from high temperatures, which can lead to dehydration and destruction of its structure. ## Storage Specimens should be stored under stable conditions, in closed, padded collector boxes, to protect them from dust, physical damage, and humidity changes. They should not be exposed to direct sunlight.