Sinjarite
Chemical formula: CaCl<sub>2</sub>·2H<sub>2</sub>O
Sinjarite is a rare, water-soluble calcium chloride, occurring as colorless or white, fibrous aggregates and crusts.
Properties
- Mohs hardness
- 1.5
- Luster
- Vitreous
- Streak
- White
- Density
- 1.81
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification The key diagnostic feature of sinjarite is its immediate reaction to water – the mineral dissolves in it. Its appearance as delicate, white, acicular or fibrous aggregates is also characteristic. It is very soft and light. In field conditions, its identification is difficult due to its instability. ## Distinguishing from Similar Minerals Sinjarite can be confused with other soluble halides or sulfates, such as halite, sylvite, or gypsum (especially its fibrous variety, selenite). It differs from halite and sylvite by its crystal habit (acicular, not cubic) and crystallographic system. It differs from gypsum by its significantly lower hardness and solubility in water. A taste test is not recommended, but sinjarite has a bitter and salty taste, unlike purely salty halite. ## Crystal Forms Sinjarite crystallizes in the form of very fine, elongated, acicular or hair-like crystals. It typically forms radial or tangled fibrous aggregates, as well as dusty coatings and crusts.
Geological environment
## Genesis Sinjarite is an evaporitic mineral. It forms in extremely dry, desert climates as a result of the evaporation of solutions rich in calcium chloride. It forms as a dehydration product of antarcticite (hexahydrate of calcium chloride) or by direct crystallization from brines at temperatures above 40°C. It occurs in desert clays and marls. ## Mineral Associations This mineral co-occurs with other evaporites, primarily halite (rock salt), as well as antarcticite, gypsum, and calcite. ## Localities The most important and type locality for sinjarite is the Sinjar Mountains in Iraq, where it was discovered. Its presence has also been confirmed in a few other localities with similar, extremely dry climates, including the Atacama Desert in Chile.
Rarity
Very rare
For collectors
## Quality Criteria The collector appeal of sinjarite specimens is very specific and mainly stems from its extreme rarity. Most valued are specimens with well-formed, visible-to-the-naked-eye aggregates of acicular or fibrous crystals, abundantly covering a fragment of the host rock. Due to the nature of the mineral, purity and transparency are not key criteria. The most important factor is the quantity and form of the sinjarite itself on the specimen. ## Popular Localities The only source of collector specimens is the type locality – Jabal Sinjar in Iraq. Specimens from this location are extremely difficult to acquire and represent a great rarity in the collector's market.
Care and storage
## Cleaning The mineral is extremely sensitive to water and moisture. **It must absolutely not be cleaned wet**, as it will completely dissolve. The only permissible method for dust removal is very careful use of a soft, dry brush or gentle blowing with compressed air from a distance. ## What to Avoid Avoid all contact with water, water vapor, and other liquids. The mineral is highly hygroscopic and absorbs moisture from its surroundings, leading to its disintegration. It should be protected from humid air, temperature changes causing condensation, and direct sunlight, which can accelerate dehydration processes. ## Storage Sinjarite specimens require storage in conditions of controlled, very low humidity. The best solution is a sealed container (e.g., a "perky box") with a desiccant (silica gel) placed inside. The container should be stored at a stable room temperature, away from sources of heat and light.