Motukoreaite

Chemical formula: Mg₆Al₃(OH)₁₈[Na(H₂O)₆](S⁶⁺O₄)₂·₆H₂O

Motukoreaite is a very rare, hydrated magnesium, sodium, and aluminum sulfate, forming small, hexagonal plates with a pearly luster.

## Characteristics Motukoreaite is a mineral belonging to the wermlandite group. It occurs as very small, hexagonal, tabular crystals, which typically form rosette-like or spherulitic aggregates. Due to the small size of the crystals, its features are most often observed in aggregates, which can cover rock surfaces in the form of thin coatings or crusts. ## Physical Properties This mineral is extremely soft, with a Mohs hardness of only 1-1.5, meaning it can be scratched with a fingernail. It is also very light, with a density of approximately 1.48 g/cm³. It is characterized by a pearly luster on cleavage surfaces and a translucent nature. ## Colors and Varieties Motukoreaite is most often colorless or white. It can also take on yellowish hues. No named varieties of this mineral are distinguished. ## History and Name The mineral's name comes from its discovery locality and refers to the Maori name for Browns Island (Motukorea) in the Hauraki Gulf, near Auckland, New Zealand. It was described and approved as a new mineral in 1977 by K. A. Rodgers, J. E. Chisholm, R. J. Davis, and C. S. Nelson. ## Uses Motukoreaite has no industrial application and is solely an object of interest for collectors specializing in rare minerals and scientists.

Properties

Mohs hardness: 1-1.5
Luster: Pearly
Streak: White
Density: 1.48
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Motukoreaite is identified by its characteristic, small, hexagonal crystals forming rosette aggregates. Key features include extreme softness (hardness 1-1.5), pearly luster, low density, and occurrence in a specific geological environment – as an alteration product of basalt in contact with seawater. ## Distinguishing from Similar Minerals It can be confused with other secondary minerals forming white coatings, such as some zeolites or clay minerals. Distinguishing it usually requires advanced analytical methods, such as X-ray diffraction (XRD). For collectors, verifying the specimen's locality of origin is crucial. ## Crystal Forms It forms very small, thin, tabular crystals with a hexagonal outline. These crystals almost always occur as aggregates – rosette-like, spherulitic, or forming thin crusts and coatings.

Geological environment

## Genesis Motukoreaite is a secondary mineral, formed as a result of low-temperature alteration of volcanic rocks (mainly basalt) by seawater. It forms in gas vesicles and fractures in basaltic tuffs and palagonites. ## Mineral Associations It often co-occurs with other secondary minerals, such as calcite, aragonite, gypsum, as well as various minerals from the zeolite group (e.g., phillipsite) and clay minerals. ## Localities The most important and type locality is Browns Island (Motukorea) in New Zealand. It is also known from several other localities worldwide where similar geological conditions prevail, including Oahu Island in Hawaii (USA) and some places in Italy and Germany.

Rarity

Very rare

For collectors

## Quality Criteria The quality of motukoreaite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. Specimens with well-formed, distinct rosettes covering a significant area of the rock matrix are most valued. Crystal size is crucial, although they rarely exceed fractions of a millimeter. Purity and lack of damage to delicate structures are also very important. ## Popular Localities By far the most classic and valued specimens come from the type locality – Browns Island (Motukorea) in New Zealand. Specimens from this location are a benchmark for collectors of this mineral.

Care and storage

## Cleaning Motukoreaite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly risky. If necessary, a very soft brush can be used to remove loose dust, performing extremely careful movements. ## What to Avoid Contact with water, which can dissolve or damage the mineral, must be absolutely avoided. It should also be protected from all chemicals, acids, and detergents. Due to its low hardness, it is susceptible to scratches and abrasions from almost any other material. ## Storage Specimens should be stored in closed, stable containers (e.g., "micromount" type) to protect them from mechanical damage, dust, and humidity changes. They should not be exposed to direct sunlight or areas of high humidity.