Antarcticite

Chemical formula: CaCl<sub>2</sub>·6H<sub>2</sub>O

Antarcticite is a rare, hygroscopic calcium chloride that is liquid at room temperature, crystallizing only at low temperatures.

## Characteristics Antarcticite is a hydrated calcium chloride, a mineral known for its extreme hygroscopicity and very low crystallization temperature. At room temperature (above 25°C), it is a liquid – a brine. To solidify and crystallize, it requires temperatures significantly below zero. The crystals are colorless, acicular, or prismatic. Due to its properties, it is an extremely difficult mineral to preserve in collections and is rarely found outside its natural environment or a laboratory. ## Physical Properties Antarcticite crystals are very soft and brittle, with a Mohs hardness of only 2-3. They have a vitreous luster and are transparent. Their density is low, approximately 1.715 g/cm³. The most characteristic feature is strong hygroscopicity – the mineral actively absorbs moisture from the surroundings, leading to its dissolution (deliquescence) at temperatures above 25°C. ## Colors and Varieties Antarcticite is colorless, sometimes with a whitish or yellowish tint caused by impurities. No named varieties of this mineral are distinguished. ## History and Name The mineral was discovered in 1963 in Don Juan Pond in Wright Valley, Victoria Land, Antarctica. The name, given in 1965 by Tetsuya Torii and Joyo Ossaka, directly refers to the continent where the discovery was made. Don Juan Pond is one of the most saline bodies of water on Earth, allowing it to remain liquid even at temperatures as low as -50°C. ## Uses Antarcticite has no industrial applications. Its significance is purely scientific and as a collector's item, although due to its properties, it is an extremely rare and difficult object to maintain in collections.

Properties

Mohs hardness
2-3
Luster
Vitreous
Streak
White
Density
1.715
Cleavage
Perfect on {1011} and {0112}
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification The key diagnostic feature of antarcticite is its behavior depending on temperature and humidity. At low temperatures, it forms colorless, acicular crystals, which turn into a liquid (brine) at room temperature. Its extreme hygroscopicity is unique. The taste is bitter and salty. ## Distinguishing from Similar Minerals Antarcticite can be confused with other hygroscopic halides, such as halite (rock salt) or sylvite. However, halite and sylvite are not as strongly hygroscopic and do not spontaneously dissolve in humid air to the same extent. Furthermore, unlike antarcticite, they are stable in solid form over a wide range of temperatures. ## Crystal Forms Antarcticite crystallizes in elongated, acicular, or slender prismatic forms. It often forms radial aggregates or fibrous masses. Well-formed, freestanding crystals are rare.

Geological environment

## Genesis Antarcticite forms by precipitation from extremely saline waters (brines) under conditions of very low temperature and an extremely dry climate. Its formation is associated with the evaporation of waters in closed sedimentary basins in polar or high-mountain environments. ## Mineral Associations This mineral co-occurs with other evaporites, such as halite, gypsum, and celestine. At its discovery site in Antarctica, it was accompanied by these very minerals. ## Localities The most important and type locality is Don Juan Pond in Antarctica. It has also been found as efflorescences in caves in Pretoria (South Africa), in brines on the bottom of the Red Sea, in Bristol Dry Lake in California (USA), and in lake sediments on the Taman Peninsula in Russia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of an antarcticite specimen primarily depends on its preservation and form. Well-formed, transparent acicular crystals or their radial aggregates are most desirable. Since this mineral is extremely unstable, it is crucial that the specimen is properly secured in an airtight container, often in the original brine from which it crystallized. The mere fact of possessing a confirmed, crystalline specimen makes it unique. ## Popular Localities By far the most known and valued source of specimens is the type locality – Don Juan Pond in Antarctica. Specimens from other locations, such as Bristol Dry Lake in California, are also found in collections but do not have the same status as those from Antarctica.

Care and storage

## Cleaning This mineral essentially does not require cleaning, as any contact with water or even humid air at positive temperatures will cause it to dissolve. Specimens must be stored in hermetically sealed containers. ## What to Avoid It is absolutely necessary to avoid: - Temperatures above 0°C, and ideally, it should be stored in freezing conditions (below -25°C) to prevent melting. - Any moisture and contact with air of standard humidity, which leads to deliquescence (dissolution). - Contact with chemicals. ## Storage The only safe storage is a hermetically sealed container, placed in a freezer at a stable, low temperature. Display in home conditions is practically impossible without specialized, cooled, and dehumidified equipment.

External references

Sources

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