Iowaite

Chemical formula: Mg₆Fe³⁺₂(OH)₁₆Cl₂·4H₂O

A rare magnesium iron hydroxyhalide, forming blue-green or yellowish, waxy aggregates that fade and dehydrate in air.

## Characteristics Iowaite is a rare mineral from the hydroxyhalide group, belonging to the hydrotalcite supergroup. It typically forms massive, cryptocrystalline or fibrous aggregates, as well as lamellae and rosettes. Its appearance is distinctive – it has a waxy or greasy luster and often occurs as veins or fillings in serpentinite rocks. Freshly discovered specimens have an intense blue-green color, which, however, quickly fades upon exposure to air, changing to greenish-yellow, yellowish-brown, and even orange hues due to dehydration and oxidation. ## Physical Properties Iowaite is a very soft mineral, with a hardness of only 1.5 on the Mohs scale, meaning it can be scratched with a fingernail. It is light, with a density of approximately 2.13 g/cm³. The lamellae and fibers of the mineral are flexible but inelastic. It exhibits perfect cleavage in one direction, parallel to the basal plane of the crystals. ## Colors and Varieties The dominant and most desired color of iowaite is blue-green to blue. Under the influence of water loss (dehydration) and oxidation processes, its color changes to greenish-yellow, yellowish-brown, and even orange-red. No named varieties of this mineral are distinguished. ## History and Name The mineral was discovered in 1965 in drill core samples from Sioux County, Iowa, USA. Its name comes directly from the state where its type locality is situated. It was described by D. W. Kohls, D. L. Graf, and I. E. Odom in 1967. ## Uses Iowaite has no industrial applications. It is solely of interest to collectors of rare minerals and scientific institutions.

Properties

Mohs hardness
1.5
Color
Bluish green
Luster
Waxy
Streak
White
Density
2.11
Cleavage
Perfect basal cleavage
Fracture
Uneven
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Key diagnostic features of iowaite include its characteristic blue-green color (on fresh surfaces), very low hardness (1.5 on the Mohs scale), and waxy or greasy luster. An important clue is its instability in dry air, leading to a color change to yellowish or brownish. Its occurrence in serpentinites in association with chlorite and brucite is also a strong indicator. ## Distinguishing from Similar Minerals Iowaite is sometimes confused with other minerals from the hydrotalcite supergroup, such as stichtite (purple-pink) or pyroaurite (blue-green to yellow). Pyroaurite is very similar but usually has slightly higher hardness. Definitive differentiation often requires chemical analysis (XRD, EDS) to confirm the presence of chlorine, which is a key component of iowaite. ## Crystal Forms Well-formed crystals are extremely rare. Iowaite typically forms very fine, hexagonal lamellae that aggregate into massive, cryptocrystalline, or waxy masses. It often occurs as fibrous veins, spherulites, or rosette-like aggregates.

Geological environment

## Genesis Iowaite is a secondary mineral, formed as a result of low-temperature hydrothermal processes or serpentinization of ultramafic rocks, such as peridotites and dunites. It forms in veins and fractures within these rocks, often in an environment rich in brine solutions that provide the necessary chlorine. ## Mineral Associations This mineral most commonly co-occurs with serpentine minerals (antigorite, lizardite, chrysotile), as well as brucite, chlorite, magnetite, dolomite, calcite, and chromite. ## Localities The most important and classic iowaite localities worldwide include its type locality in Sioux County, Iowa, USA (in drill cores); the Palabora deposits in the Republic of South Africa, from which numerous collector specimens originate; the chromite mine in Okayama Prefecture, Japan; and occurrences in Russia (Kola Peninsula) and Canada (Jeffrey Mine in Quebec).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with an intense, blue-green or pure blue color, which indicates that the mineral has not undergone dehydration. Rich aggregates in the form of veins cutting through the host rock (serpentinite) are highly prized, as are rare specimens with visible rosettes or spherulites. Contrast with a dark matrix enhances the visual appeal of the specimen. ## Popular Localities Undoubtedly, the most well-known and valued collector specimens come from the Palabora deposit in Limpopo Province (RSA). Specimens from this locality are characterized by their beautiful blue color and often occur as attractive veins in serpentinite.

Care and storage

## Cleaning Iowaite is extremely delicate and sensitive to water. It should absolutely not be washed in water, which can damage it and accelerate the dehydration process. To remove dust, a very soft brush can be used, or dust can be carefully blown off with compressed air from a distance. ## What to Avoid Avoid contact with water and all chemicals. The mineral is very sensitive to changes in humidity and temperature. It loses water in dry air, causing an irreversible color change from blue to yellow or brown. It should be protected from direct sunlight and heat sources. ## Storage Iowaite specimens must be stored in sealed, airtight containers (e.g., "perky box" type or membrane boxes) to prevent dehydration and maintain their original color. It is best to store them in stable conditions, away from light and heat sources.

External references

Sources

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