Ghiaraite

Chemical formula: CaCl<sub>2</sub>·4H<sub>2</sub>O

Ghiaraite is a naturally occurring hydrated calcium chloride, forming colorless, acicular crystals, found as a product of volcanic exhalations.

## Characteristics Ghiaraite is a halide mineral, chemically hydrated calcium chloride (CaCl₂·4H₂O). It occurs as colorless, transparent crystals with an acicular or hair-like habit, often forming radial aggregates or crusts. It is a very delicate mineral, sensitive to changes in humidity. ## Physical Properties Ghiaraite crystals exhibit a vitreous luster. Due to their nature, they are very soft and brittle. The mineral is hygroscopic, meaning it readily absorbs moisture from the air, which can lead to its dissolution. ## History and Name The mineral was named in honor of Professor Giancarlo Ghiara (born 1949), an Italian mineralogist and curator of the Real Museo Mineralogico in Naples, in recognition of his contributions to the study of Vesuvius mineralogy. It was approved by the IMA in 2011, and its discovery was described in 2013. ## Uses Due to its rarity, instability, and small crystal size, ghiaraite has no industrial applications. It is solely an object of scientific interest and a collector's item for specialized micromount mineral collectors.

Properties

Mohs hardness
1.5
Luster
Vitreous
Streak
White
Density
1.84
Cleavage
Perfect on {101}
Fracture
Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Its appearance as delicate, colorless needles forming radial aggregates is characteristic. A key diagnostic feature is its instability in humid air and solubility in water. It occurs as a product of volcanic activity. ## Distinguishing from similar minerals It can be confused with other similar, acicular secondary minerals formed in volcanic environments, such as halotrichite or epsomite. Differentiation requires chemical analysis (EDS/XRD) or observation of its reaction to moisture. Unlike sulfates (halotrichite, epsomite), ghiaraite is a chloride. ## Crystal forms It forms very fine, elongated crystals with an acicular or hair-like habit. These crystals most often occur as radial or chaotic aggregates, as well as delicate crusts on the surface of the host rock.

Geological environment

## Genesis Ghiaraite is a mineral of volcanic origin, formed as a result of exhalation (sublimation) of volcanic gases. It crystallizes directly from hot vapors escaping from fumaroles, at temperatures below 45°C, in a chlorine-rich environment. ## Mineral associations It co-occurs with other fumarolic minerals, such as halite, sylvite, and rare chlorides, e.g., sinjarite (CaCl₂·2H₂O). ## Localities The only confirmed locality of this mineral in the world (type locality) is the Vesuvius-Somma volcanic complex in Campania, Italy. It was found there in exhalative products dated to the 1944 eruption.

Rarity

Very rare

For collectors

## Quality criteria For ghiaraite, the most important criterion is the richness and aesthetics of the acicular crystal aggregates. Specimens with clearly formed, radial groupings on a small fragment of host rock are highly valued. Due to the microscopic size of the crystals, specimens are mainly evaluated under magnification. The purity and transparency of the needles also increase the specimen's value.

Care and storage

## Cleaning The mineral is water-soluble and very hygroscopic. It must absolutely not be wet-cleaned. Dust removal can only be done using a very soft brush or careful use of a photographic air blower. ## What to avoid Avoid contact with water, water vapor, and humid air, which cause its dissolution. Protect it from all chemicals. It is sensitive to elevated temperatures. ## Storage Ghiaraite specimens must be stored in airtight, tightly sealed containers (e.g., "perky box" type) with a desiccant (silica gel). They should be kept at a stable room temperature, away from direct sunlight.

Sources

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