Mooreite

Chemical formula: Mg₁₅(S⁶⁺O₄)₂(OH)₂₆·8H₂O

Mooreite is a rare, hydrated magnesium sulfate, forming colorless or white, platy crystals with a pearly luster.

## Characteristics Mooreite is a mineral from the sulfate group, chemically a basic hydrated magnesium sulfate. It occurs as small, platy or bladed crystals, often grouped into rosette-like or radial aggregates. Crystals are usually colorless to white, sometimes with a pale green or yellowish tint. A characteristic feature is their perfect cleavage in one direction, which gives the crystal surfaces a pearly luster. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2.5. It is light, with a density of about 2.47 g/cm³. Crystals are transparent to translucent. The luster on cleavage surfaces is distinctly pearly, while on other surfaces it is vitreous. ## Colors and Varieties Mooreite is usually colorless or white. Some specimens may exhibit a pale green or pale yellow coloration, likely due to impurities. No named varieties of this mineral are distinguished. ## History and Name Mooreite was discovered in the Sterling Hill Mine in Ogdensburg, Sussex County (New Jersey, USA). It was described in 1929 by Lawson H. Bauer and Harry Berman. The mineral is named in honor of Gideon E. Moore (1842-1895), an American chemist who was the first to perform chemical analyses of many minerals from the Franklin deposit in New Jersey. ## Uses Due to its rarity, small crystal size, and low hardness, mooreite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from the Franklin-Sterling Hill deposit.

Properties

Mohs hardness
3
Color
Colourless, light tan; colourless in transmitted light.
Luster
Pearly, Vitreous
Streak
White to colorless
Density
2.47
Cleavage
On {010}, perfect.
Fracture
Micaceous
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature of mooreite is its habit in the form of thin, platy crystals, often in radial aggregates. Also characteristic are the strong, pearly luster on surfaces of perfect cleavage and very low hardness (2.5 on the Mohs scale). It reacts with acids. ## Distinguishing from Similar Minerals Mooreite can be confused with other white or colorless secondary minerals with a pearly luster, such as brucite, talc, or gypsum. It is distinguished from gypsum by its crystal habit and co-occurrence with minerals from the Franklin deposit. It differs from brucite and talc in crystal form and occurrence environment; brucite is an oxide and talc is a silicate, while mooreite is a sulfate. ## Crystal Forms Crystals are platy, flattened parallel to the cleavage plane, with a hexagonal or octagonal outline. They often form fan-shaped, radial, or rosette-like aggregates, as well as thin coatings and efflorescences on other minerals.

Geological environment

## Genesis Mooreite is a secondary hydrothermal mineral, forming in the oxidation zone of zinc deposits. It forms as a result of the alteration of primary ore minerals at low temperatures. It is most commonly found in fractures and voids within zinc ores. ## Mineral Associations This mineral occurs in association with other rare secondary minerals typical of the Franklin-Sterling Hill deposit. It most commonly co-occurs with fluoborite, hydrohetaerolite, zincite, willemite, franklinite, as well as calcite and pyrochroite. ## Localities Mooreite is a very rare mineral. For many years, it was known only from its discovery site – the Sterling Hill Mine in Ogdensburg, New Jersey, USA, which is its type locality. Its occurrence has also been confirmed in the Långban mine in Sweden and the Ilímaussaq complex in Greenland.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp crystals forming aesthetic, radial or rosette-like aggregates. Transparency and clarity of crystals, as well as the absence of mechanical damage, are important. A contrasting matrix, for example with dark franklinite, significantly enhances the visual appeal and value of the specimen. ## Popular Localities By far the most known and valued mooreite specimens come from its type locality – the Sterling Hill Mine in New Jersey, USA. Specimens from this location are considered classic and serve as a benchmark for this mineral.

Care and storage

## Cleaning Mooreite is a very delicate, soft mineral, soluble in acids. It should only be cleaned mechanically, using a very soft brush to remove dust. Avoid contact with water, which can damage the crystal surfaces. ## What to Avoid Absolutely avoid contact with water, acids, and other chemicals. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. Due to its low hardness, it is very susceptible to scratches and mechanical damage. ## Storage Mooreite specimens should be stored in stable conditions, preferably in closed, padded boxes or display cases, to protect them from dust, mechanical damage, and humidity changes. It should be kept away from harder minerals that could scratch it.

External references

Sources

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