Chloraluminite
Chemical formula: AlCl<sub>3</sub>·6H<sub>2</sub>O
Chloraluminite is a rare, water-soluble aluminum halide, occurring as colorless or white crystals and efflorescences in volcanic environments.
Properties
- Mohs hardness
- 1
- Luster
- Vitreous
- Streak
- White
- Density
- 1.65
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification The key diagnostic feature of chloraluminite is its immediate and complete solubility in water. Its delicate, acicular or woolly aggregates occurring in a specific environment (volcanic fumaroles) are also characteristic. The taste is described as sharp and astringent, but tasting is highly inadvisable and dangerous. ## Distinguishing from similar minerals Chloraluminite can be confused with other soluble halides or sulfates formed under similar conditions, such as halotrichite or sylvite. It differs from sylvite by its crystal habit (acicular instead of cubic) and crystallographic system. From fibrous sulfates (e.g., halotrichite), it can be distinguished by a test for chlorides after dissolving a sample (reaction with silver nitrate), but this requires destroying a fragment of the specimen. ## Crystal forms This mineral crystallizes in the form of very fine, elongated crystals with an acicular or capillary habit. These crystals often form tangled, woolly or felt-like aggregates, as well as crusts and efflorescences on rocks.
Geological environment
## Genesis Chloraluminite is a mineral of volcanic origin. It forms by sublimation from hot gases (exhalations) in fumaroles, where hydrogen chloride reacts with aluminum-rich rocks. It crystallizes at temperatures above 100°C in an anhydrous environment. ## Mineral associations It most commonly co-occurs with salammoniac, hematite, and native sulfur. It is also accompanied by halite, sylvite, and other rare chlorides and fluorides formed in fumarolic environments. ## Localities The most important and classic locality is the Vesuvius volcanic complex in Italy, where it was discovered. It has also been reported in exhalation products from Mount Fuji in Japan and on the Kamchatka Peninsula in Russia. These are the only confirmed and well-documented localities for this rare mineral.
Rarity
Very rare
For collectors
## Quality criteria The most highly prized chloraluminite specimens are those with rich, well-preserved, "fluffy" aggregates of acicular crystals on a piece of host rock (matrix). Due to the mineral's instability, the state of preservation is a key factor – specimens must not show signs of dissolution or clumping due to moisture. The size and aesthetics of the matrix also affect value. ## Popular localities Specimens from the historical locality of Vesuvius in Italy are by far the most sought after by collectors. Material from this site holds "classic" status and is most highly valued on the market.
Care and storage
## Cleaning The mineral **must not be cleaned** with any liquids, including water or alcohol. Any contact with moisture will cause its immediate dissolution. Specimens can only be cleaned mechanically, using a very delicate, dry brush or careful blowing with compressed air from a distance. ## What to avoid Contact with water, water vapor, and humid air must be strictly avoided. The mineral is extremely hygroscopic and absorbs moisture from the surroundings, leading to its deliquescence (dissolution in absorbed water). It should not be touched with bare hands, as skin moisture can damage it. It must be protected from temperature changes, which can cause water vapor condensation. ## Storage Chloraluminite specimens require storage in hermetic, tightly sealed containers (e.g., "perky box" type) with a desiccant (e.g., silica gel) to ensure a completely dry environment. The container should be placed in a temperature-stable location, away from direct sunlight.