Beusite

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

Beusite is a rare phosphate mineral of the graftonite group, a manganese phosphate, found as granular or massive aggregates in granitic pegmatites.

## Characteristics Beusite is a rare mineral belonging to the graftonite group, chemically classified as a manganese phosphate. It typically forms anhedral (lacking well-formed crystal faces) grains or massive aggregates, which can reach sizes up to 15 cm. It is rarely observed in the form of thick, tabular crystals. This mineral is brittle and often shows the presence of numerous fractures or inclusions. ## Physical Properties Beusite is characterized by a hardness of 5 on the Mohs scale. Its luster is vitreous to resinous, and the mineral is translucent to opaque. The density ranges from 3.68-3.71 g/cm³. ## Colors and Varieties The typical color of beusite is brown, dark brown to almost black. On fresh surfaces, it may be lighter, darkening upon oxidation. No named varieties are distinguished. ## History and Name The mineral is named in honor of Alexey Alexandrovich Beus (1923-2009), a Russian mineralogist and geochemist who made significant contributions to the study of granitic pegmatites. The mineral was first described in 1968 based on material from the White Cap pegmatite in Custer County, South Dakota, USA. ## Uses Beusite has no industrial application. Its significance is limited to the scientific and collecting spheres, as a rare representative of the graftonite group.

Properties

Mohs hardness
5
Luster
Resinous to vitreous
Streak
Light brown
Density
3.68-3.71
Cleavage
Good on {010}
Fracture
Uneven to subconchoidal
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Beusite is identified by its brown color, resinous luster, relatively high density, and occurrence in granitic pegmatites. Massive, granular aggregates are characteristic. Good cleavage in one direction can be helpful in identification, although it is not always easy to observe in granular aggregates. ## Distinguishing from Similar Minerals Beusite is difficult to distinguish from other minerals of the graftonite group (e.g., graftonite) without advanced chemical analyses (EDS/WDS). It can be confused with other dark phosphates found in pegmatites, such as triplite, arrojadite, or especially sarcopside, with which it often forms intergrowths. Definitive differentiation usually requires chemical composition analysis. ## Crystal Forms Beusite crystals are extremely rare. It usually occurs in massive, granular, or irregular aggregates embedded in the host rock. The rare described crystals had a thick-tabular habit.

Geological environment

## Genesis Beusite is a primary phosphate mineral crystallizing in granitic pegmatites, particularly in their intermediate zones and cores. It forms under conditions of relatively low oxygen fugacity. ## Mineral Associations This mineral often co-occurs with other phosphates, such as graftonite, triplite, sarcopside, lithiophilite, and triphylite. It is also accompanied by typical pegmatite minerals: quartz, microcline, albite, muscovite, and beryl. ## Localities The most important beusite localities worldwide are the pegmatites in the Black Hills region of South Dakota (USA), especially in the White Cap, Bull Moose, and Tip Top mines, where it was discovered. It is also known from pegmatites in Argentina (e.g., San Luis), Brazil (Minas Gerais), Finland, Germany (Hagendorf-Süd), and Russia (Kola Peninsula).

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, though rare, crystals are most valued by collectors. Rich, massive aggregates with an intense, dark brown color, contrasting with a light rock background (e.g., with quartz or albite), are also highly prized. Association with other rare phosphates is also important. ## Popular Localities Classic and most sought-after specimens come from the type localities in South Dakota, USA (White Cap and Bull Moose mines). Material from these localities is considered referential for this mineral species.

Care and storage

## Cleaning Beusite specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Avoid water and any chemical agents, as the mineral can oxidize and change color. ## What to Avoid Avoid contact with water, acids, and other chemicals. The mineral is sensitive to moisture and oxidation processes, which can lead to its degradation and change in appearance. It should not be heated or subjected to ultrasonics. ## Storage It is recommended to store beusite specimens in dry conditions, preferably in tightly sealed containers or display cases away from moisture. Due to its brittleness, it should be protected from impacts and contact with harder minerals.

Sources

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