Rosemaryite

Chemical formula: ◻NaMn²⁺(Fe³⁺Al)(PO₄)₃

Rosemaryite is a rare mineral from the phosphate group, forming dark, vitreous crystals, valued by collectors specializing in rare minerals.

## Characteristics Rosemaryite is a complex phosphate of sodium, manganese, iron, and aluminum, belonging to the alluaudite group. It occurs as small, tabular or prismatic crystals, which can form radial aggregates. Its crystals are typically very small, rarely exceeding 1 mm in length. This mineral is brittle. ## Physical Properties Rosemaryite is characterized by a vitreous luster. Its Mohs hardness is approximately 5, and its density ranges from 3.62 to 3.69 g/cm³. It is a transparent to translucent mineral. ## Colors and Varieties This mineral ranges in color from dark green to black. Some specimens may exhibit weak pleochroism in shades of green and brown. No varieties are distinguished for it. ## History and Name Rosemaryite was first described in 1979 by Paul B. Moore and Takaharu Araki. The mineral is named in honor of Rosemary Ann Williams (b. 1942), an American amateur mineralogist and collector, who first drew attention to this mineral in material collected from the Tip Top Mine in South Dakota, USA. ## Uses Due to its rarity and small crystal size, rosemaryite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness
4-4.5
Color
Dark olive-green, dark brown
Luster
Vitreous
Streak
Greenish-gray
Density
0
Cleavage
{010} {<mi>1</mi01>}, by analogy with ferrowyllieite
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of rosemaryite is practically impossible and requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Preliminary identification is based on its dark green to black color, vitreous luster, and occurrence in association with other phosphates in granitic pegmatites. ## Distinguishing from Similar Minerals Rosemaryite is visually indistinguishable from other dark minerals of the alluaudite group, such as alluaudite itself, ferroalluaudite, or hagendorfite. Definitive differentiation is possible only through detailed chemical analysis. ## Crystal Forms It forms small, tabular or prismatic crystals, often grouped into radial or rosette aggregates. Crystals rarely reach a size that allows for observation with the naked eye.

Geological environment

## Genesis Rosemaryite is a secondary mineral, formed in complex granitic pegmatites. It forms as a result of hydrothermal or metasomatic processes, replacing earlier, primary phosphate minerals such as triphylite or lithiophilite. ## Mineral Associations This mineral co-occurs with other phosphates, such as jahnsite-(CaMnFe), rockbridgeite, strengite, ludlamite, vivianite, as well as with quartz, albite, and muscovite. ## Localities The most important and best-documented rosemaryite localities worldwide include: - Tip Top Mine, near Custer, South Dakota, USA (type locality). - Angarf-Sud Mine, near Tazenakht, Ouarzazate Province, Morocco. - Buranga locality in Rwanda.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a rosemaryite specimen is primarily determined by the size and development of its crystals, which is a rarity. The most prized specimens are those with clearly visible, even if small, radial crystal aggregates on a rock matrix. Due to its dark color, color intensity is less significant. Crucial factors also include a well-documented locality and analytically confirmed mineral identity. ## Popular Localities The most known and valued specimens come from the type locality - the Tip Top Mine in South Dakota, USA. Specimens from Morocco and Rwanda are also sought after by collectors specializing in the systematics of phosphate minerals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to potential reactivity with water, it is recommended to avoid wet cleaning. If necessary, use a minimal amount of isopropyl alcohol and dry the specimen immediately. ## What to Avoid Avoid contact with water, acids, and other chemicals. The mineral is brittle, so it must be protected from impacts and vibrations. It should not be heated or subjected to ultrasound. ## Storage Rosemaryite specimens, being rare and often microscopic, are best stored in specialized "micromount" boxes or in small, padded containers that protect them from mechanical damage and dust.

External references

Sources

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