Ferrorosemaryite

Chemical formula: &#9744;NaFe<sup>2+</sup>(Fe<sup>3+</sup>Al)(PO<sub>4</sub>)<sub>3</sub>

Ferrorosemaryite is a rare phosphate mineral of the wyllieite group, being the ferrous (Fe²⁺) analog of rosemaryite.

## Characteristics Ferrorosemaryite is a very rare mineral from the wyllieite group, belonging to the phosphates. It forms small, granular aggregates or occurs as massive infillings. Individual crystals are too small to be seen with the naked eye. The mineral is characterized by a dark green to black color and a vitreous luster. ## Physical Properties Ferrorosemaryite is a relatively hard mineral, with a Mohs hardness of 4. It has a density of approximately 3.53 g/cm³. It exhibits a vitreous luster and is opaque. The streak is grayish-green. ## Colors and Varieties This mineral occurs in dark green to black. No varieties have been distinguished. ## History and Name Ferrorosemaryite was first described in 2008 by Anthony R. Kampf, Paul B. Moore, Ian M. Steele, and Joe Marty. Its name refers to its chemical composition – it is an analog of rosemaryite with dominant ferrous iron (ferro) – and to rosemaryite itself. The name rosemaryite, in turn, comes from Rosemary, the daughter of one of the discoverers of that mineral. It was approved by the International Mineralogical Association (IMA) under number IMA2007-049. The type specimen comes from the Blue-Scherader mine in the Custer area, South Dakota, USA. ## Applications Due to its extreme rarity and small size of occurrences, ferrorosemaryite has no practical or commercial applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Gray-green
Density
3.53
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of ferrorosemaryite is possible almost exclusively through advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). In field conditions or in a collection, it is visually unrecognizable. The dark green to black color, vitreous luster, and occurrence in granitic pegmatites are clues, but insufficient for certain identification. ## Distinguishing from Similar Minerals Ferrorosemaryite is visually indistinguishable from other dark phosphates of the wyllieite group, such as wyllieite itself, rosemaryite, or ferrowyllieite. It can also be confused with many other dark accessory minerals found in pegmatites, e.g., some tourmalines (schorl) or triplite. Certain distinction requires specialized laboratory tests. ## Crystal Forms This mineral forms subhedral (poorly formed) to anhedral (unformed) grains up to 1 mm in size. It usually occurs as granular aggregates.

Geological environment

## Genesis Ferrorosemaryite is a primary mineral, crystallizing in the late stages of the evolution of complex granitic pegmatites, rich in phosphorus and lithium. It forms in zones of differentiated pegmatites, in the presence of other phosphates. ## Mineral Associations In the type locality (Blue-Scherader mine, USA), ferrorosemaryite co-occurs with minerals such as quartz, albite, muscovite, schorl, triplite, goyazite, visnevit, jahnsite-(CaMnFe), and fluorapatite. ## Localities It is an extremely rare mineral, known from only a few locations worldwide. Besides the type locality at the Blue-Scherader mine in South Dakota (USA), its occurrence has also been reported in an LCT (lithium-cesium-tantalum) type pegmatite in Angulos dos Touros, Portugal.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral or one occurring as very small grains, the main criterion for value for collectors is the confirmation of its identity by chemical analysis or XRD. The most desirable specimens are those where ferrorosemaryite is as well-formed, visible, and richly accumulated on the rock matrix as possible. Association with other rare phosphate minerals is also crucial. The size of individual grains, although always small, also affects the evaluation of the specimen. ## Popular Localities The only source of collectible specimens, though extremely rare, is the type locality – the Blue-Scherader mine in Custer County, South Dakota, USA.

Care and storage

## Cleaning Due to the extreme rarity and typically small size of specimens, mechanical cleaning is not recommended. If absolutely necessary, a soft brush can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid all chemical agents, especially acids, which can damage the mineral. Do not expose it to ultrasound. Protect from high temperatures and sudden temperature changes. ## Storage Ferrorosemaryite specimens, being microscopic or very small, should be stored in specialized "micromount" boxes or sealed containers, protecting them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight.

Sources

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