Manasseite

Chemical formula: Mg<sub>6</sub>Al<sub>2</sub>CO<sub>3</sub>(OH)<sub>16</sub>·4H<sub>2</sub>O

Manasseite is a rare mineral of the hydrotalcite group, forming small, hexagonal platelets and rosettes, and is a polymorph of sjögrenite.

## Characteristics Manasseite is a mineral of the hydrotalcite group, being a hexagonal polymorph of sjögrenite. It forms very small, thin, hexagonal, tabular crystals, which often arrange into rosettes or lamellar aggregates. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. It usually occurs as coatings and aggregates on other minerals. ## Physical Properties Manasseite is a very soft mineral with a hardness of about 2 on the Mohs scale. It has a pearly luster on cleavage surfaces and a vitreous luster on fracture surfaces. It is transparent to translucent. Its density is approximately 2.13 g/cm³. ## Colors and Varieties It is most often colorless, white, bluish-white, or pale yellow. It does not have defined commercial or color varieties. ## History and Name The mineral was first described in 1941 by Clifford Frondel. Its name commemorates the German mineralogist and paleontologist Ernesto Manasse (1875-1922) from the University of Pisa in Italy, who was the first to study material from the type locality, incorrectly identifying it as hydrotalcite. ## Uses Manasseite has no industrial applications. It is solely of interest to collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
2
Luster
Pearly
Streak
White
Density
2.13
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Identifying manasseite based on visual characteristics is practically impossible without specialized equipment. X-ray diffraction (XRD) is crucial, as it allows distinguishing it from polymorphic sjögrenite and other minerals of the hydrotalcite group. A characteristic chemical feature is its violent reaction with acids. ## Distinguishing from Similar Minerals Manasseite is macroscopically indistinguishable from sjögrenite, with which it is a polymorph. Sjögrenite crystallizes in the trigonal system, while manasseite crystallizes in the hexagonal system, which can only be determined by diffraction methods. It can also be confused with other minerals of the hydrotalcite group, such as hydrotalcite or pyroaurite, from which it differs in chemical composition and structural parameters. ## Crystal Forms It forms very small, thin, hexagonal (six-sided) platelets. These crystals often group into rosettes, spherulitic aggregates, or form thin, lamellar coatings.

Geological environment

## Genesis Manasseite is a secondary mineral, formed as a result of low-temperature hydrothermal processes and serpentinization processes of ultramafic rocks (e.g., peridotites). It forms in veins cutting serpentinites or as an alteration product of other minerals in skarns and ore deposits. ## Mineral Associations It most often co-occurs with its polymorph, sjögrenite. It is also accompanied by other minerals typical of serpentinite and skarn environments, such as serpentine (antigorite, lizardite), brucite, magnetite, chromite, dolomite, calcite, and aragonite. ## Localities The most important and classic manasseite localities are in Sweden, in the Långban and Nordmark mines (Värmland), from which the type material originates. It is also known from Vermiglio in Trentino (Italy) and from several localities in the USA, including Cedar Hill Quarry in Lancaster County (Pennsylvania) and the Tysfjord river area in Norway.

Rarity

Rare

For collectors

## Quality Criteria The quality of a manasseite specimen is primarily determined by the abundance and development of microcrystals, as well as its association with other minerals. The most desirable specimens are those with clearly visible (under magnification) rosettes or groups of hexagonal platelets on a contrasting matrix. Due to the microscopic nature of the crystals, their "purity" or "color" are of secondary importance compared to the morphology of the aggregates. ## Popular Localities Classic and most prized specimens, often serving as a standard for this mineral, come from Swedish mines in the Värmland region (Långban, Nordmark). Specimens from these historical localities are sought after by collectors specializing in mineral systematics.

Care and storage

## Cleaning Manasseite specimens are extremely delicate and soft, so they must be handled with the utmost care. Mechanical cleaning is highly inadvisable. If absolutely necessary, the specimen can be carefully rinsed in distilled water, then left to air dry completely without heating. ## What to Avoid Manasseite is sensitive to acids, which cause it to effervesce violently and decompose. Contact with any chemicals, ultrasound, and high temperatures, which can cause water loss from its structure, should be avoided. As a very soft mineral, it is susceptible to scratches and mechanical damage. ## Storage It is recommended to store specimens in separate, padded collector boxes to protect them from dust, light, and mechanical damage. Avoid storage in areas with fluctuating humidity.

Sources

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