Beusite-(Ca)

Chemical formula: CaMn<sup>2+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>

A rare phosphate mineral, found in granitic pegmatites, forming aggregates of brown grains.

## Characteristics Beusite-(Ca) is a rare mineral belonging to the phosphate group, specifically to the graftonite group, of which it is the calcium analog. It typically occurs as anhedral (irregular) grains forming aggregates, rarely exhibiting any crystalline forms. Its appearance is inconspicuous, and specimens are most often brown to reddish-brown in color. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a vitreous to resinous luster. It is a relatively dense mineral, with its density calculated from the chemical formula and unit cell parameters being 3.85 g/cm³. It is brittle and translucent. ## Colors and Varieties Beusite-(Ca) occurs in shades of brown, from reddish-brown to dark brown. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – it is a member of the beusite series, in which calcium (Ca) is the dominant cation in one of the structural sites. It was recognized by the International Mineralogical Association (IMA) in 1998. Its discovery and description are associated with studies of phosphates in pegmatites. ## Uses Beusite-(Ca) has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare representative of the phosphate group.

Properties

Mohs hardness
5
Luster
Vitreous to Resinous
Streak
White
Density
3.85
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying beusite-(Ca) based on visual characteristics is very difficult and often impossible without advanced research. Key is determining the geological environment – occurrence in granitic pegmatites in association with other phosphates. Features such as brown color, resinous luster, and hardness of approximately 5 can be indicative but are not unique. Final identification requires chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Beusite-(Ca) is visually almost identical to other minerals from the graftonite group, such as graftonite or beusite itself. It can also be confused with many other brown minerals found in pegmatites, e.g., some garnets (spessartine), triplite, or sarcopside. Differentiation without specialized equipment is practically impossible. ## Crystal Forms This mineral primarily forms massive, granular, or irregular aggregates. It does not develop well-formed crystals (it is anhedral).

Geological environment

## Genesis Beusite-(Ca) is a mineral of magmatic origin, crystallizing in the late stages of the evolution of granitic pegmatites, rich in phosphorus and lithium. It forms as a primary mineral in zones of varied composition. ## Mineral Associations It most often co-occurs with other phosphates, such as triplite, lithiophilite, triphylite, as well as with quartz, microcline, albite, and muscovite. Its presence is an indicator of specific chemical conditions prevailing during pegmatite crystallization. ## Localities The most important and best-documented localities of beusite-(Ca) are in the USA, in South Dakota, in pegmatite mines such as White Cap Mine, Tip Top Mine, and Big Chief Mine in Custer County. It is also known from localities in Argentina (San Luis province) and China (Altai, Xinjiang Autonomous Region).

Rarity

Rare

For collectors

## Quality Criteria The collector's appeal of beusite-(Ca) specimens is limited due to its inconspicuous appearance and lack of well-formed crystals. The most prized are rich aggregates of intense, reddish-brown color, clearly identified, and originating from classic localities. Association with other, more aesthetic pegmatite minerals is crucial. The value of a specimen is enhanced by an accompanying chemical analysis result confirming its identity. ## Popular Localities The most known and valued specimens by collectors come from pegmatites in South Dakota (USA), which is the type locality for this mineral.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush or paintbrush to remove dust. Due to possible reactivity with acids, all chemical agents should be avoided. The use of water is not recommended. ## What to Avoid Contact with acids and other chemicals that may damage or destroy the mineral must be strictly avoided. It should not be subjected to ultrasound or sudden temperature changes. As a brittle mineral, it is susceptible to mechanical damage. ## Storage Beusite-(Ca) specimens should be stored in stable conditions, in separate, padded collector's boxes to prevent scratches and chipping. They should be protected from moisture and chemical contamination.

Sources

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